Refactor random url generation into its own method

Previously, endpoint URL were generated randomly before sending endpoint
requests to the Keystone server. Now that Keystone is validating input
on incoming requests, URLs have to match a regular expression in order
to be considered valid. This change makes the endpoint URLs compliant
for the endpoint request.

Change-Id: I365e651632fc4952a483655e51f3958598e059dd
3 files changed