Unify label_and_version in legacy_service_gateway apis

This is a new patch set for https://github.com/cloudfoundry/cloud_controller_ng/pull/3
 - use label_and_version rather than service_label 
 - when creating a new service offering, check whether label includes extra dash postgresql-9.1 is ok while postgres-sql-9.1 is not
 - update the unit test

=== Test plan ====
Unit-test passed
Yeti-test:
  ccng(v1) passed
  ccng(v2) passed
Ad-hoc test:
 recovery test passed