Use tarballs in requirements.txt

Because using repositories breaks tests in tuskar-ui-extras and is generally
discouraged.

Also, remove empty lines from between imports, becase now tuskarclient is
and external project according to pep8.

Change-Id: I54c7ea994bc0e4167dab00af9be503c9f3e3dc06
Merge "Use tarballs in requirements.txt"