Fix up dependency list.

The ``prettytable`` secondary dependency was updated upstream.  This
caused installation to fail because a primary dependency
(python-novaclient) specified an upper limit on its prettytable
requirement.

It turns out, only python-novaclient really needs prettytable, so this
change removes Bang's explicit dependency (which was a workaround for
python-reddwarfclient's failed packaging).
Bump version to 0.7.1