Update optional requirements

Robottelo has been depending on a fork of nose_xunitmp (maintained by @blrm)
instead of the upstream version (maintained by @Ignas). However, the changes in
the fork have been merged back into upstream.

Make Robottelo depend on upstream again.
Automatically generate even more API docs

Auto-generate API docs for the `tests` module, in addition to the `robottelo`
module. Make git ignore the files which sphinx-apidoc generates.
Updated 'stubbed' decorator to allow 'reason'.

Updated the 'stubbed' decorator to allow passing a 'reason' string. If
none is passed, then default to NOT_IMPLEMENTED.
Disabling all Organization deletion tests.

Deleting organizations can lead to some really serious issues, so DEV is
disabling it for now. See
https://bugzilla.redhat.com/show_bug.cgi?id=1106563 for more information.
Merge pull request #884 from omaciel/disable-org-deletion

Disable org deletion
Merge pull request #883 from Ichimonji10/dependencies

Update optional requirements
Merge pull request #882 from Ichimonji10/docs

Automatically generate even more API docs