Correct exception handling when create aggregate

when create an aggregate, InvalidAggregateAction might be raised,
this patch translates the InvalidAggregateAction to HTTPBadRequest.
Also, 2 unnecessary logs was removed becuase log is not output in
most BadRequest.

Change-Id: I3dac808d8edab6118e347eb5d78b96f96b9d40ca
Remove duplicate method

Duplicate method(_do_test_create_instance_above_quota)
are found in compute/test_servers.py. Remove it.

Change-Id: I0753992cadc40adce40999bb5ae8ecd503bd53bc
Merge "Remove duplicate method"
Merge "Correct exception handling when create aggregate"