cifs.upcall: clean up logging and add debug messages

cifs.upcall: clean up logging and add debug messages

Change the log levels to be more appropriate to the messages being
logged. Error messages should be LOG_ERR and not LOG_WARNING, for
instance.

Add some LOG_DEBUG messages that we can use to diagnose problems with
krb5 upcalls. With these, someone can set up syslog to log daemon.debug
and should be able to get more info when things aren't working.

Signed-off-by: Jeff Layton <jlayton@redhat.com>