RestForwarderServletModuleIT: Add a cache wildcard endpoint test

Which fails if inadvertently removing that wildcard suffix from the
served cache endpoint string in RestForwarderServletModule.

The cache/project_list endpoint support is implemented in such a way
that a 204 gets returned by the servlet no matter if the served
endpoint string ends with a wildcard or not.

Change-Id: I7d88cfd88385e08e8b25813980115ff5504aded8