[autotest] Add --noinstall option to deployment_test.

In deployment_test, the servo install step is time-consuming, and
running that step provides little coverage when testing the script.
So, add an option to allow skipping the installation step for
purposes of testing the script.

BUG=None
TEST=run deployment_test --noinstall, see it complete quickly

Change-Id: I19104039852d01d635fb2fc8ac97dcad126bf02a
Reviewed-on: https://chromium-review.googlesource.com/302000
Commit-Ready: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Mungyung Ryu <mkryu@google.com>
2 files changed