Added a function `enable_rhrepo_and_fetch_repoid` and few fixes.

Added `enable_rhrepo_and_fetch_repoid` function, to group many
steps required for syncing RedHat Repos.

The `sync` function under `Repository` Class now returns a task_id.

Added and Fixed many docstrings.

Updated the import related to cloning manifests.

Added test related to syncing RedHat Repository

Few fixes after Repository.sync returns task_id
This URL does not exist, and I rather regret including this blurb in so many modules. I'd just drop this paragraph completely, and make this a one-line docstring:

    """Unit tests for the ``sync`` paths."""