package_name ignored if getting version from git

[Stephen Finucane]

I'm using 'pbr.packaging.get_version()' to get the version of a package that is not installed. Because the package is not installed, pbr falls back to git to get the version numbers. However, it seems to fail to check the 'package_name' argument passed to this.

    >>> from pbr import packaging
    >>> packaging.get_version('openstackdocstheme')
    '1.20.0'
    >>> packaging.get_version('nova')
    '1.20.0'
    >>> packaging.get_version('testssdfsdfdsfs')
    '1.20.0'