Add missing isolated_cred cleanup to savanna tests

This commit adds a missing call to the tearDownClass in the base savanna
test class. Without this call every time the savanna tests run with
tenant isolation enabled the resources created will never be cleaned up.

Closes-Bug: #1275003

Change-Id: I69bafb5a9149f7c49390fc33f27629a8caeb5f9f
make testing neutron api extensions optional

When the Neutron API extension that test case needs is unsupported
by Neutron plugin running, the test case will be skipped.

Change-Id: Ie3b0f94ea084076ccc10d6a141c9120bf9900395
Closes-Bug: #1270244
Define py27 assertFoo methods for py26

Frequent issue a test case is failing with py26,
because the used assert method like the assertGreaterEqual
is not defined.

Adding unittest2.TestCase to the base testclass when running
tempest with py26.

Change-Id: I5184fe88485b611c033e81f82177060460da7f1e
Merge "Define py27 assertFoo methods for py26"
Merge "Add missing isolated_cred cleanup to savanna tests"
Merge "make testing neutron api extensions optional"