Use owner rather than filename format in choosing cred cache files

Use owner rather than filename format in choosing cred cache files

Signed-off-by: Glenn Machin <gmachin@sandia.gov>
Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
Some installations use different name formats for their credentials
caches.  Instead of checking that the uid is part of the name, just
make sure that uid is the owner of the file.
This is a modification of the original patch from Glenn.
Signed-off-by: Neil Brown <neilb@suse.de>