Failing sky tests should not make tree red

The sky tests are too unstable right now to make the buildbot red.
Temporarily make a failing sky test step stay green while the underlying
issues are debugged and fixed. The log and flakiness dashboard output
will still reflect what actually happened during a run.

TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/746133004

mojo/tools/mojob.py

diff --git a/mojo/tools/mojob.py b/mojo/tools/mojob.py
index dc2de5f..03f48a8 100755
--- a/mojo/tools/mojob.py
+++ b/mojo/tools/mojob.py
@@ -157,7 +157,10 @@
     command.append('--test-results-server')
     command.append(args.test_results_server)
 
-  return subprocess.call(command)
+  subprocess.call(command)
+  # Sky tests are currently really unstable, so make the step green even if
+  # tests actually fail.
+  return 0
 
 
 def run_pytests(args):