mcollective puppetrun provider can't find puppet-agent mco binary
In puppet 4 (puppet-agent AIO packages) the location of the mco binary has changed.
The mcollective puppetrun provider tries to find the mco binary here.
fixes #15043 - Fix puppet 4 mco search path
In puppet 4, (AIO packaging), binaries can be found in
(`/opt/puppetlabs/bin/mco` is actually a symlink to
`/opt/puppetlabs/puppet/bin/mco`, but `/opt/puppetlabs/bin` is what's
added to PATH in `/etc/profile.d/puppet-agent.sh` so is probably the
path that should be searched.)