Hammer CLI

When using hammer to create a host on a Libvirt provider, the --compute-attributes option accepts a "start" key to tell hammer if the new host must be immediately started.
The key is described as a boolean value, but when using "start=true" the new host is not started.
The new host is started, instead, if using "start=1".

Also "true" should be accepted, to be more user-friendly.
A different solution would be to only accept 1 and 0, but then the help output should be updated accordingly to better express this, and also any docs around, like the Success Story (http://projects.theforeman.org/issues/3297) which has an example containing "start=true".