power_Consumption: Fix failure to load test page.

Presently this test is failing quite frequently because the initial
sanity check for the local web server returns '' instead of the
document title 'Test page'.

Patch adds call to WaitForDocumentReadyStateToBeComplete method after
Sanity test instead of directly querying via EvaluateJavaScript result
for expected value.

Patch also refactors chrome instance from intialize method to run_once
so we no longer need to explicitly kill instance in cleanup.

Finally a few pylint bugfixes to appease the pre-commit-check.

TEST=run power_Consumption on samus and it completes successfully.

Change-Id: I97d277ba1a2e6a46ae9bceb4a7cef1867489c93c
Reviewed-on: https://chromium-review.googlesource.com/271321
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
(cherry picked from commit 0ac98a72887d9eba096caf2f24dffe68190374b2)
Reviewed-on: https://chromium-review.googlesource.com/273550
1 file changed