In the DEB package build I saw the following:

13:20:11 npm WARN lifecycle TheForemanDevDeps@1.17.0~postinstall: cannot run in wd %s %s (wd=%s) TheForemanDevDeps@1.17.0 node ./script/npm_install_plugins.js /var/lib/workspace/workspace/packaging_build_deb_coreproject/arch/armv8/label/debian/os/xenial/debian/xenial/build-foreman/foreman-1.17.0

And on my workstation I'm getting:

$ npm install

> TheForemanDevDeps@1.17.0 postinstall /home/mmoll/mystuff/gitrepos/theforeman/foreman
> node ./script/npm_install_plugins.js

child_process.js:635
    throw err;
    ^

Error: Command failed: /home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.rb
    at checkExecSyncError (child_process.js:592:13)
    at execSync (child_process.js:632:13)
    at webpackedDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:44:10)
    at getPluginDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:50:41)
    at packageJsonDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:54:37)
    at Object.<anonymous> (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/npm_install_plugins.js:6:1)
    at Module._compile (module.js:624:30)
    at Object.Module._extensions..js (module.js:635:10)
    at Module.load (module.js:545:32)
    at tryModuleLoad (module.js:508:12)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! TheForemanDevDeps@1.17.0 postinstall: `node ./script/npm_install_plugins.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the TheForemanDevDeps@1.17.0 postinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

tail of the log:

1786 verbose unlock done using /home/mmoll/.npm/_locks/staging-74de5aa0c3c5414e.lock for /home/mmoll/mystuff/gitrepos/theforeman/foreman/node_modules/.staging
1787 silly install runPostinstallTopLevelLifecycles
1788 silly build TheForemanDevDeps@1.17.0
1789 info linkStuff TheForemanDevDeps@1.17.0
1790 silly linkStuff TheForemanDevDeps@1.17.0 has /home/mmoll/mystuff/gitrepos/theforeman as its parent node_modules
1791 verbose linkBins TheForemanDevDeps@1.17.0
1792 verbose linkMans TheForemanDevDeps@1.17.0
1793 silly install TheForemanDevDeps@1.17.0
1794 info lifecycle TheForemanDevDeps@1.17.0~install: TheForemanDevDeps@1.17.0
1795 silly postinstall TheForemanDevDeps@1.17.0
1796 info lifecycle TheForemanDevDeps@1.17.0~postinstall: TheForemanDevDeps@1.17.0
1797 verbose lifecycle TheForemanDevDeps@1.17.0~postinstall: unsafe-perm in lifecycle true
1798 verbose lifecycle TheForemanDevDeps@1.17.0~postinstall: PATH: /usr/lib/node_modules/npm/bin/node-gyp-bin:/home/mmoll/mystuff/gitrepos/theforeman/foreman/node_modules/.bin:/home/mmoll/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:/home/mmoll/.rvm/bin:/home/mmoll/bin:/home/mmoll/.rvm/bin
1799 verbose lifecycle TheForemanDevDeps@1.17.0~postinstall: CWD: /home/mmoll/mystuff/gitrepos/theforeman/foreman
1800 silly lifecycle TheForemanDevDeps@1.17.0~postinstall: Args: [ '-c', 'node ./script/npm_install_plugins.js' ]
1801 silly lifecycle TheForemanDevDeps@1.17.0~postinstall: Returned: code: 1  signal: null
1802 info lifecycle TheForemanDevDeps@1.17.0~postinstall: Failed to exec postinstall script
1803 verbose stack Error: TheForemanDevDeps@1.17.0 postinstall: `node ./script/npm_install_plugins.js`
1803 verbose stack Exit status 1
1803 verbose stack     at EventEmitter.<anonymous> (/usr/lib/node_modules/npm/node_modules/npm-lifecycle/index.js:280:16)
1803 verbose stack     at emitTwo (events.js:125:13)
1803 verbose stack     at EventEmitter.emit (events.js:213:7)
1803 verbose stack     at ChildProcess.<anonymous> (/usr/lib/node_modules/npm/node_modules/npm-lifecycle/lib/spawn.js:55:14)
1803 verbose stack     at emitTwo (events.js:125:13)
1803 verbose stack     at ChildProcess.emit (events.js:213:7)
1803 verbose stack     at maybeClose (internal/child_process.js:927:16)
1803 verbose stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:211:5)
1804 verbose pkgid TheForemanDevDeps@1.17.0
1805 verbose cwd /home/mmoll/mystuff/gitrepos/theforeman/foreman
1806 verbose Linux 4.13.0-1-amd64
1807 verbose argv "/usr/bin/node" "/usr/bin/npm" "install" 
1808 verbose node v8.7.0
1809 verbose npm  v5.4.2
1810 error code ELIFECYCLE
1811 error errno 1
1812 error TheForemanDevDeps@1.17.0 postinstall: `node ./script/npm_install_plugins.js`
1812 error Exit status 1
1813 error Failed at the TheForemanDevDeps@1.17.0 postinstall script.
1813 error This is probably not a problem with npm. There is likely additional logging output above.
1814 verbose exit [ 1, true ]

standalone execution:

$ node script/npm_install_plugins.js 
child_process.js:635
    throw err;
    ^

Error: Command failed: /home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.rb
    at checkExecSyncError (child_process.js:592:13)
    at execSync (child_process.js:632:13)
    at webpackedDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:44:10)
    at getPluginDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:50:41)
    at packageJsonDirs (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/plugin_webpack_directories.js:54:37)
    at Object.<anonymous> (/home/mmoll/mystuff/gitrepos/theforeman/foreman/script/npm_install_plugins.js:6:1)
    at Module._compile (module.js:624:30)
    at Object.Module._extensions..js (module.js:635:10)
    at Module.load (module.js:545:32)
    at tryModuleLoad (module.js:508:12)