dafs: log to stderr when running salvageserver in client mode

dafs: log to stderr when running salvageserver in client mode

When the -client option is given to the salvageserver, print
Log() messages to stderr instead of losing them.

Change-Id: I065e8136db9a8cc241639fbe34607db884751b95
Reviewed-on: http://gerrit.openafs.org/11729
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>