LU-196 set $PTLDEBUG, $SUBSYSTEM and $DEBUG_SIZE values on every node

LU-196 set $PTLDEBUG, $SUBSYSTEM and $DEBUG_SIZE values on every node

The current set_default_debug_nodes() could not pass the values of
$PTLDEBUG, $SUBSYSTEM and $DEBUG_SIZE to the remote nodes while they
are specified from the command line on the local node. This patch is
to fix this issue.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: I85922c67e7c68a5ea3e9ba7fc1cbf6516907c285
Reviewed-on: http://review.whamcloud.com/593
Tested-by: Hudson
Reviewed-by: Chris Gearing <chris@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>