Add homedir to plist search path to enable agents provided by the user

 * Add tests for service provider ghlaunchd
Sudo to user if user is defined

method user is not implemented
New test for sudo, but fails with

Puppet::Error: Command plutil is missing
Fixed the tests for user, implemented user
Run launchctl as boxen_user if a LaunchAgent is given

 * Read boxen_user from facter
 * Add /Users/{boxen_user}/Library/LaunchAgents to launchd dirs