Re-enable a lot of cinder scheduler tests

This highlight and fixes a NoneType exception in the schedulers
_get_weighted_candidates method

This was originally added to get around the fact that the filter tests
required that cinder was correctly installed on the system. But the
is_cinder_installed condition always returning False and this hid
problems of old packages been installed in our system. Also
930f5891b0815e1b49b9b2cc840e0c24b2796e84 added the setup.py automatically
to run_tests.sh so we can remove this.

See https://review.openstack.org/#/c/20213/ for history.

Fixes bug: 1213226

Change-Id: I86fee802c0543355471ddbd712e52ccec750cea0
Merge "Re-enable a lot of cinder scheduler tests"