DAFS: allow salvager to detect whether FSYNC server is DAFS

DAFS: allow salvager to detect whether FSYNC server is DAFS

in order to enable the right commands and print the right errors,
query for DAFS-only FSYNC op.
doesn't use bozo InstanceInfo as it's possible you can run fileserver
outside of bos.

Change-Id: Ib94f7b3a2960cd493f110af4d5dee7e97a6493c9
Reviewed-on: http://gerrit.openafs.org/3486
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>