_inhibitmarkers: turn the result from generator into a list
A generator object is always True, we have to turn it into a list in order to be
able to use it in the tests. Before this patch we were rewriting the
'obsinhibit' file all the time, this had a performance impact especially on
repository where transaction are expensive (hooks, cache invalidation, etc).
Writing this file less often have a minor effect on test where a stripped
changeset does not get removed from the obsinhibit file is still inhibited when
unbundled back. I think this is fine and I'm moving forward.