Add RHN subscription_manager module

The subscription_manager module acts as a wrapper to the command
'subscription-manager'.  The subscription-manager utility allows users
to manage RHN registration, subscription and yum repositories from the
Red Hat Entitlement platform.

Currently, this module supports the following sub-commands:
 * config
 * [un]register
 * subscribe
Updated examples and documentation
Merge branch 'subscription_manager' of git://github.com/jlaska/ansible into devel
Fixup doc YAML