Remove locals() from messages in virt/disk/api.py

No functional changes, just removing something which annoyed me
when I read the code.

Change-Id: Ia2d232d6ee2e61d3785b57798391474b8e99dee1
Merge "Remove locals() from messages in virt/disk/api.py"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp