When a requirement url is used don't lose it.

Previously it seems like we lost requirement
urls and then downloading said requirment url
would fail (since the url is typically provided
if the package isn't on pypi yet). This seems
to be happening for the latests nova requirement
which seems to try to pull in a special oslo
config version.

Change-Id: I30acea47f07f6d189fd63ab9e90434f1eb4e4e2d
Merge "When a requirement url is used don't lose it."