Fixes the alternate driver invocation

This fixes the getattr call on the storage alternate driver to pass an instance
of the storage alternate driver.  This makes the glance driver work again.

Co-Authored-By: Chris Alfonso <calfonso@redhat.com>
Docker-DCO-1.1-Signed-off-by: Ian Main <imain@redhat.com> (github: imain)
Merge pull request #2 from calfonso/fix_alternate_storage_getattr

Fixes the alternate driver invocation