Make git cookbook robust in the face of missing some of the repo tarballs.

Instead of dying on the first missing git repo tarball, just skip on
to the next ones of we were not able to download the tarball to stage
for serving.
Merge pull request #21 from VictorLowther/pull-req-release-pebbles-master-8f21319d8693626bd2e77f301f9477dda04f0118

Make Tempest much more amenable to being run without using PFS. [1/2]