viced: avoid useless core if shutdown during initialization

viced: avoid useless core if shutdown during initialization

Avoid leaving an unnecessary core file when the fileserver is
shutdown while still attaching volumes.  The bosserver issues
SIQUIT to shutdown the fileserver which leaves a core file by
default.

Register the fileserver shutdown signal handler earlier in the
fileserver initialization, before the long running volume
attachment is started. The volume package shutdown has been
changed to allow the VShutdown to gracefully abort the volume
attachment (or pre-attachment for DAFS).

FIXES 124485

Change-Id: Ic22e68afb7bcc54ad956b2ae093375f29b969191
Reviewed-on: http://gerrit.openafs.org/764
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>