aklog: check ccache errors in get_user_realm

aklog: check ccache errors in get_user_realm

if there's an error finding the specified ccache, don't
bother continuing.

Reviewed-on: http://gerrit.openafs.org/5069
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 09d1d8575ce96ef945a4fd8a99a0347f4e258c1e)

Change-Id: I4b18cae14a9b620ea62d62eebc0b62f83f67a84a
Reviewed-on: http://gerrit.openafs.org/5072
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>