remote_access.sh: Use opportunistic, automatic ControlMaster

Change remote_access to automatically attempt to share a single SSH
connection.  This significantly speeds up remote_access since we avoid
all of the connection establishment the majority of the time.

This shaves a few seconds off of update_kernel.

BUG=None
TEST=Try updating a kernel

Change-Id: I33f0cd856c9e15d25adb4c28389d833596798cb4
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/410244
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed