Unifiy service label in legacy service gateway

Split the service_label (e.g. postgresql-9.2) to get the label (e.g. postgresql) for we should use the latter one to look up the models.

ccng (v2) plan 100/200 yeti-test passed
ccng (v1) plan 100       yeti-test passed
cc           plan free       yeti-test passed

ad-hoc test:
    - service recovery test(to test update_handle api): passed.

original story:
    There is a bug in legacy_service_gateway
    From below two lines, we need a label w/o version to retrive service_auth_token in validate_access
    https://github.com/cloudfoundry/cloud_controller_ng/blob/master/lib/cloud_controller/legacy_api/legacy_service_gateway.rb#L175, 
    https://github.com/cloudfoundry/cloud_controller_ng/blob/master/lib/cloud_controller/legacy_api/legacy_service_gateway.rb#L127
     
    But, from below these lines, service gateway will provide a service_label (label with version)
    https://github.com/cloudfoundry/vcap-services-base/blob/master/lib/base/asynchronous_service_gateway.rb#L93
    https://github.com/cloudfoundry/vcap-services-base/blob/master/lib/base/asynchronous_service_gateway.rb#L480
    https://github.com/cloudfoundry/vcap-services-base/blob/master/lib/base/catalog_manager_v2.rb#L491

 So, use servie_label.split('-') will definitely get "postgresql" from service_label "postgresql-9.0"

Change-Id: I39e9a12aad934367a54d090e8027a88ffd4e12f0