Move *_ec2_* tests in test_db_api to own test case.

There is *_ec2_* tests in old mixed DbApiTestCase.
This patch moves them to its own test case Ec2TestCase.

Also missing tests added to new test case.

blueprint db-api-tests

Change-Id: I2d14cd36873c736411f6cc587aa52dbdb1296445
Merge "Move *_ec2_* tests in test_db_api to own test case."