Add a test for CloudStack compute driver which verifies that driver throws an
exception if user instantiates the driver correctly, but doesn't provider host
and path argument.
Add a provider constant for CloudStack loadbalancer driver and expose it through
get_driver.
Modify CloudStackLB driver to throw if user instantiates it directly, but
doesn't pass in host and path.
Add a test case for ninefold loadbalancer driver.
Use unittest2.
Update CHANGES.