Separate negative tests for test_quotas

Move negative tests from test_quotas.py to test_quotas_negative.py.
Some test cases in test_quotas.py which test the exceptions should
also be considered as negative test.
Move them to test_quotas_negative.py

Partially implements blueprint negative-test-files

Change-Id: Ib30e5b81d6c9519b6968aa8d6255fc10812dec3e
2 files changed