clean the unittest2.

We have used the testtools instead of unittest2. So when we run
tempest, if it require unittest2 packages. We should look into
why it need unittest2, and can we use testtools instead? Not just
add unittest2 in pip-require simply. And new test added into
tempest should use testtools other than unittest2.

Change-Id: Ica02779b16434f9d64b0bb655c44251301b94492
Make isolated volume tests have unique tenant

The isolated credential volume tests need to have unique tenant
names otherwise when the test_volume_types_extra_specs tests are
run in parallel they step on each other.

Change-Id: I7f6d81af97cd48522ea52477a3afe9564f717d89
Merge "clean the unittest2."