Bug 994986 - Remove 'rhc cartridge' because it conflicts with other aliases

Ruby 1.8.7 has random order hashes, and depending on how the commands load the
'rhc cartridge' alias (to list) and 'rhc cartridges' were getting confused. 
Since we don't alias the root command in other scenarios, I've removed 'rhc
cartridge' as an alias.

@fabianofranz review please