[autotest] abstract.py: log system load before starting master-ssh

It is believed that builder load contributes to VMTest banner exchange
flake, which occurs almost exclusively during either master-ssh
connection establishment, or during the first ssh-ping after booting
a VM. This CL logs the system load right before each master-ssh
connection establishment.

BUG=chromium:254166
TEST=None

Change-Id: Ie6f203230ac90ae4b5e3b8dd5cc589c37f0d0beb
Reviewed-on: https://chromium-review.googlesource.com/172929
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
1 file changed