Added task to clean RHSM and fixed Capsule task.

First off, fixed the capsule installer task which was missing a space in
the command.

Second, handled tasks with `Boolean` arguments which are by default
parsed as `String` by `Fabric`.

Lastly, improved `client_registration_test` to remove the `Web Server`
group and perform total clean up at the end.
Merge pull request #14 from omaciel/clean-rhsm

Added task to clean RHSM and fixed Capsule task.
Add install_prerequisites task

This task will ensure that the system have all installation
prerequisites in place