Add new test wait event methods to SiteHost, and use them.

Added test_wait_for_sleep(), test_wait_for_resume(),
test_wait_for_shutdown(), and test_wait_for_boot() to SiteHost.
These methods replace wait_up() and wait_down() to use customized
timeouts and generate a test failure if the required condition
doesn't occur.

Updated selected servo-based tests to use the new methods.

BUG=chromium-os:29896
TEST=run the changed tests

Change-Id: Ic21f97f0672b0c16504028a4ed4533b24f4e5e0f
Reviewed-on: https://gerrit.chromium.org/gerrit/21150
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Scott Zawalski <scottz@chromium.org>
Commit-Ready: Richard Barnette <jrbarnette@chromium.org>
6 files changed