(RE-2222) Push gems to internal server on release

This commit adjusts the ship_gem utility to include a try for pushing
the completed gem to the stickler host, currently rubygems.delivery.puppetlabs.net.
The host name can be overwritten using the environment variable GEM_HOST.
If it fails it puts an error for user to check if they can access the server and have stickler installed.
Is there any way you could make this louder? E.g. maybe some sweet ascii art about a warning?