[remoting-test] Fix It2Me browser test failures.
Currently, we wait for 30s for the session to be connected but we
didn't specify any timeout when waiting for session failure.
As a result, the default timeout of 5 seconds is used.
This CL also makes the test stricter by only failing the test when
the current mode matches the expected failure mode.
Those tests are passing before, this suggests that it takes longer
now for an IT2ME connection to fail, which may be related to the
recent signaling change.
BUG=486872
Review URL: https://codereview.chromium.org/
1178313004
Cr-Commit-Position: refs/heads/master@{#334980}