Return a cell name from afsconf_LookupServer

Return a cell name from afsconf_LookupServer

Previously, afsconf_LookupServer could not meaningfully return a cell
name, since a char* was passed in for realCellName, and
afsconf_GetAfsdbInfo was expecting the value of the pointer to change.
Change afsconf_LookupServer to take a char**, and pass realCellName by
reference, so we can get a cell name back.

Change-Id: Ib945fcb4be482ee155cdd1dcd62fe577c002082d
Reviewed-on: http://gerrit.openafs.org/1039
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>