viced: Make the config directory path global

viced: Make the config directory path global

Store the location of the configuration directory in a global
variable, rather than hardcoding it in multiple locations in the file.
This makes it easier to write unit tests for portions of the fileserver,
and is a step towards producing a fileserver that can be run from
within the test suite.

Change-Id: I0ee1d9bed084472b1e29b9c559a8726f867f91e4
Reviewed-on: http://gerrit.openafs.org/7585
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>