fssync-debug: close test connection

fssync-debug: close test connection

A valid fssync-debug query <volid> command issued against
a DAFS fileserver will produce the following error messages in FileLog:

	SYNC_getCom:  error receiving command
	FSYNC_com:  read failed; dropping connection (cnt=1)

Routine dafs_prolog() issues a tentative FSYNC_VOL_LISTVOLUMES operation
to test for the presence of a DAFS fileserver.  If DAFS is detected,
we then call dafssync-debug for the original requested operation.
However, the FSYNC connection for the tentative LISTVOLUMES operation
is never closed. This results in the errors when the command completes.

Close the test connection.

Change-Id: I3c987289408407ba38cd184b7518e72ee1ae9cfc
Reviewed-on: http://gerrit.openafs.org/10476
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>