bugzilla: switch svc_name to old-bugzilla

switch Bugzilla's svc_name config, used
in Apache config template, over to
old-bugzilla, for after the phab migration

untested, also needs changes in BZ admin UI
to go with it

Change-Id: I3e7c3513fa94b11ec7979b785a5d6039f5dc3c0f