Limit formatting routes when adding resources

By default, routes.mapper.Mapper.resource adds a bunch of formatted
routes that accept anything after a '.'. Our spec says only .xml
and .json are accepted so limit the formatting to those valuse.

This allows identifiers with a '.' in urls. A few tests were added
to the extensions test to prove that .xml and .json are stripped
but other values are not.

Closes-bug: #1307956
Change-Id: I8f0b4ae3b10ea93890f6506662905bd5823412f5
Merge "Limit formatting routes when adding resources"
Removes unecessary call to rbd.Image

Removed duplicate and unprotected call to rbd.Image
in rbd driver which can result in an uncaught exception
if the rbd image no longer exists.

Also added unit test for _delete_backup_snaps()

Closes-Bug: 1323203
Change-Id: I89eedb0d0276a985b4d496093df2eee2ce067ec1