Avoid long socket paths in KCM tests

The build directory path may be too long for a Unix domain socket, so
use a path in a temporary directory instead.  Reported by Ryan
Schmidt.

https://github.com/krb5/krb5/commit/35fac31b7645e14d75200d31c631a8530c9b855c
Author: Greg Hudson <ghudson@mit.edu>
Commit: 35fac31b7645e14d75200d31c631a8530c9b855c
Branch: master
 src/tests/t_ccache.py |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)