For telemetry tests, the browser needs to get access to some test api
from the mus window server, which is only exposed to clients marked as
'test' in their manifest. Instead of making default chrome-browser such a
test client, create a separate telemetry-browser catalog, which is used
when run with --use-test-config command-line flag. Instead of adding
dependency on this test catalog from the main chrome executable, create a
separate test_chrome executable that can be used for running the
telemetry tests.

BUG=704681, 721640

Review-Url: https://codereview.chromium.org/2910383002
Cr-Commit-Position: refs/heads/master@{#477326}