Adds negative tests to test_records.py

This submission adds two negative tests under
"designate/tests/test_api/test_v1/test_records.py" script.
Following are the negative tests -
1. test_create_record_invalid_ttl
2. test_update_record_negative_ttl

Change-Id: I9d1f71f9c27169a2478ad196e0eab64a7a2e93d0