webservd: Add test for basic webservd DBus API

This test asserts that webservd's manager answers the Ping()
method with "Web server is running"

BUG=chromium:451082
TEST=test_that -b link --fast 100.96.49.23 webservd_BasicDBusAPI
CQ-DEPEND=CL:242624

Change-Id: I4f2347a753467dee45ae405c58dd15390f67251c
Reviewed-on: https://chromium-review.googlesource.com/242700
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
2 files changed