auth: local realms configuration

Add krb.conf and krb.excl support to the auth cell configuration
library.  Provide a function to determine if the user is local to the
cell.  Provide a function to set the local realms during application
initialization.  These changes are intended to replace the functions
afs_krb_get_lrealm and afs_is_foreign_ticket_name.

Reviewed-on: http://gerrit.openafs.org/5744
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit f8b759b63ff938e2829fefd71059202c44e7ca13)

Change-Id: Ifb1e9cb00dedf21e82aecf66812aef3c93166d99
Reviewed-on: http://gerrit.openafs.org/10035
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>