auth: Rework afsconf_UpToDate to use CellServDB

auth: Rework afsconf_UpToDate to use CellServDB

Rework the afsconf_UpToDate check so that it uses the modifcation of
the CellServDB, and not the KeyFile to determine whether the
configuration information has been changed under us or not. afsconf
defines the CellServDB as being the single sentinel for a config
directory being changed, and our tools are careful to always touch
the CellServDB when updating anything else there.

Also, rework the _afsconf_Check() code so that it uses afsconf_UpToDate,
rather than including this logic twice.

Change-Id: I8ef5f67afbb5982bb25e12407ea5dc5dc1512840
Reviewed-on: http://gerrit.openafs.org/4203
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>