Fix files in Cinder with execute bit set

I noticed there were a number of files in the cinder/volume
directory tree that have the execute bit set for no apparent
reason.  I think in all cases it was because that was just
they way the permissions on the file were originally set based
on the user's umask settings.

This patch changes the permissions to be consistent with the other
python files in the cinder/volume directory.

Change-Id: Ib52cbe16ed426392c3b296b56b4d2592b4808e65