Added database adapter abstract service factory.

Change-Id: I35ed79abc898088c50d40467d6e64726e433e9f7
Removed redundant else statement and redundat condition in factory method.

Change-Id: Ia6882123128c1752151f4c4560cb8d1fcb57efa5
Added db.adapters section for multiple adapters configuration. Improved validation for existing adapter configuration. Updated unit test.

Change-Id: I2ae710320d34a2fb888fcce49969cb776b27b5a7