If there was a problem importing a library we would incorrectly raise
an unsupported version error:
$ glance --os-image-api-version 1 image-list
"1" is not a supported API version. Example values are "1" or "2".
We should change this to provide information on the failed import, eg:
$ glance --os-image-api-version 1 image-list
No module named badimport
We also now raise the full stacktrace in this case if '--debug' is passed
on the command line.
Change-Id: I1c687ae6c5da239090b0b7a4a855b3271a9076da
Related-bug: 1402632
1f89beb609