PHD: support use of multiple guest OS artifacts in a single run #173
Description
PHD expects a --default-guest-artifact option that specifies the default guest OS image to use for tests that don't choose a distinct disk image themselves. This means that if someone writes a change and wants to test it manually against a full suite of guest OSes, they'll have to run PHD multiple times (or script those executions, or what-have-you). It would be nice to have an option to fold together runs with multiple guest OSes.
The simplest way to do this is probably to accept multiple guest OSes on the command line and have the runner add all the replications when it converts the test inventory into a collection of tests to execute.