Update RHEL Registration

This patch updates the 00-rhel-registration script to not
not fail a stack when metadata isn't found.

Change-Id: Ie305fed79e4baadf1a03c4a3d06a23cf36e92f77
Warning when using pypi element without a mirror

Using only a local filesystem mirror could lead opaque errors.
Print a warning message in this situations.

Change-Id: I5f77151ea928868f4c441e8a1bb2eb0966b21832
Closes-Bug: #1297948
Merge "Update RHEL Registration"
Merge "Warning when using pypi element without a mirror"