Support multiple specs in scripts

[Eugene M]

The ultimate goal of Oasis is testing of microservice solutions, and this requires support for multiple spec files referenced from scripts, with names.

The suggested approach follows.

Spec reference:

specs:
  serviceA: path/to/serviceA.spec.yaml
  serviceB: path/to/serviceB.spec.yaml
  serviceC: path/to/serviceC.spec.yaml

Multiple spec files are listed with their names to use to access operations in them.

Operation reference:

operations:
  operationFoo:
    operationId: serviceA.operationFooId
  operationBar:
    operationId: serviceB.operationBarId

Operation ID includes a spec name from the specs object.