Removes dead code from trove/tests/api/root.py
Removes dead code from trove/tests/api/root.py

Reason:
- ./trove/tests/api/root.py uses undefined method
  create_mysql_connection in log_in_as_root.
- log_in_as_root is not used anywhere in any tests.

Changes:
- Removed log_in_as_root method from ./trove/tests/api/root.py

Change-Id: Ia5ab6538cab54a98b8057d0bf4c39dda9c7e3bf8
Closes-Bug: #1261174

openstack/trove,redhat-openstack/trove,redhat-openstack/trove,zhujzhuo/openstack-trove,cp16net/trove,zhangg/trove,hplustree/trove,mmasaki/trove,changsimon/trove,fabian4/trove,zhangg/trove,denismakogon/trove-guestagent,openstack/trove,fabian4/trove,changsimon/trove,mmasaki/trove,cp16net/trove,zhujzhuo/openstack-trove,denismakogon/trove-guestagent,fabian4/trove,cp16net/trove,hplustree/trove,redhat-openstack/trove,zhujzhuo/openstack-trove,mmasaki/trove,changsimon/trove