Fix images tests with tenant isolation disabled

This commit fixes the images clients for when tenant isolation is
disabled. The base image test class still had a reference to the old
auth style to get the tenant name if tenant isolation was disabled.
The recent auth_provider refactor didn't update this call so the test
would fail. This commit updates it to use the new credential dict to
get the tenant_name

Closes-Bug: #1277732

Change-Id: I42bace92e5f633d410c7a59299680caafff680f9
Fix syntax in test_load_balancer_basics._check_load_balancing

The set == {} syntax is invalid in python 2.6.

Note that even though the test is currently being skipped,
it's interpreted before the skip is executed so this fails
regardless of the skip decorator.

Closes-Bug: #1277951

Change-Id: Ic64622604a717db33555784cfe265e6af3e6dea7
Merge "Fix images tests with tenant isolation disabled"
Merge "Fix syntax in test_load_balancer_basics._check_load_balancing"
Merge branch 'master' of https://github.com/openstack/tempest