Remove redundant swap_volume tests
Remove redundant swap_volume tests

Change I36b2e2ae introduced several unit tests designed to test a fix
for a bug in swap_volume caused by BDM mangling. Change If74dd9d8
subsequently removed the BDM mangling, which made the tests
irrelevant. It also removed the only user of the source_type argument
to _test_swap_volume_driver, which was the only differentiator between
the tests, meaning the tests were all identical.

Change-Id: I851a565c06ef2dc3d3d4a530aeb7f89e58f00046

rahulunair/nova,gooddata/openstack-nova,gooddata/openstack-nova,mikalstill/nova,mahak/nova,mikalstill/nova,klmitch/nova,rahulunair/nova,mahak/nova,gooddata/openstack-nova,phenoxim/nova,klmitch/nova,klmitch/nova,rahulunair/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova,gooddata/openstack-nova,openstack/nova,mikalstill/nova,phenoxim/nova