pts: Add the -config option

pts: Add the -config option

Add the -config option to all pts commands, so that the user can set
the location of the configuration directory to use. This is primarily
provided for testing purposes, to make it simpler to build fake AFS
cells with configuration in non-standard locations.

Change-Id: I90c9c95cbf99b3853bfbe93dab1ab71c3ae7e228
Reviewed-on: http://gerrit.openafs.org/5103
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>