Add unique constraints to Service.

Added unique constraints 'uniq_services0host0topic0deleted'
('host', 'topic', 'deleted') and 'uniq_services0host0binary0deleted'
('host', 'binary', 'deleted') to Service model and migrate sripts.
Added new exceptions `ServiceTopicExists` and `ServiceBinaryExists`.
Updated service_create(). Tests updated respectively.
Tests in test_compute updated to avoid conflicts with Service UC.

blueprint db-enforce-unique-keys

Change-Id: I4d9d8cf38afc2fdca3eead65fced5001a1af209e
Merge "Add unique constraints to Service."