CF manifest: define api domain
CF manifest: define api domain

Define api domain once in metadata. This makes it easy to reference the
domain multiple times in manifest, making sure the domain is the same.

jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf