Add compatibility with Mac OS X

[jordigg]

I'll be adding Mac OS X compatibility. The code should be pretty similar to the one for Linux but changing how the service is started.
More info here: https://confluence.jetbrains.com/display/TCD9/Setting+up+and+Running+Additional+Build+Agents#SettingupandRunningAdditionalBuildAgents-AutomaticAgentStartunderMacOSx

[jordigg]

I've added Mac support over here: https://github.com/improbable-io/puppet-teamcity/tree/adding-mac-support if you want to check it out maybe we can merge it.

I have changed the service file again to work on systemd systems. The error updating was still there. We can't execute it on forking mode, we need simple. It's not the ideal way to run it but the only that works now until TeamCity changes the way the updates are performed. There's a bug open with them.

Similar things happen with Mac. On Mac if you want it to run as a service (without user login) the update doesn't work well. For now I just run it the first time manually as root to updated and then next times gets run as a service, if there's a future update it may need to be run manually again. The other option is to run it as a user and have the system set up to auto login to that user something that isn't very secure as the desktop won't be protected by password.