[autotest] Allow test to skip provision job

This change adds a new actionable label `skip_provision`. If the label
is listed in the DEPENDENCIES of a test, provision job won't run before
the test starts.
This is useful for AU test which doesn't require dut has a particular
build installed before test starts.

BUG=chromium:582353
TEST=in a devserver, modify the test control file for the dummy suite by
inject following line in the control file:
DEPENDENCIES = "skip_provision"
run dummy suite for the build:
./site_utils/run_suite.py -b veyron_jerry -i veyron_jerry-release/R50-7871.0.0 -s dummy
confirm no provision job was started, instead, reset is run.

Change-Id: I1755eb65327bd7db9f66011fbfa8f71a5e5dd8dd
Reviewed-on: https://chromium-review.googlesource.com/328392
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
3 files changed