The semver parsing in PBR doesn't handle the full suite of pep440
versions (for example: 1.2.3+foo1 is the pep440 recommended way
of handling local versions).
Since we aren't doing anything with the parsed versions anyway,
just return the string we get from importlib.
Change-Id: I0a838c639333c40db5b12cd852b921f1b1c87fed