Call Metacpan again to get the archive name to downlaod. This may or may
not be in a subdirectory.
Also generate the tarball name from this.

Not using the download_url from metacpan as it is a metacpan URL.
Make initial archive download from mirror rather than just dependencies.
Merge pull request #614 from tjnicholas/cpandownload

Fix CPAN download URL problems - correct path and use a mirror if specified