Remove the content option.

The value of content is populated based on the file parameter which is used
Ping was not working because it was not inheriting from the foreman commands.

Created a new ReadCommand for Katello which inherits from the foreman command.
Subclassed ping command from the new ReadCommand
Merge pull request #35 from bkearney/bkearney/hide-option-in-subscription

Remove the content option.
Merge pull request #57 from bkearney/bkearney/get-ping-to-work

Ping was not working because it was not inheriting from the foreman comm...
here's a boilerplate set of commands for a katello object