[autotest] Use the metrics_mock object in case chromite is not set up.

BUG=chromium:688166
TEST=unittest

Change-Id: Ic0077cb2dba75a8d820f229060f3f70f507850a1
Reviewed-on: https://chromium-review.googlesource.com/438754
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Dan Shi <dshi@google.com>
diff --git a/server/autoserv b/server/autoserv
index 54760c3..66ee795 100755
--- a/server/autoserv
+++ b/server/autoserv
@@ -27,7 +27,10 @@
 from autotest_lib.client.common_lib import utils
 from autotest_lib.client.common_lib.cros.graphite import autotest_es
 
-from chromite.lib import metrics
+try:
+    from chromite.lib import metrics
+except ImportError:
+    metrics = utils.metrics_mock
 
 try:
     from autotest_lib.puppylab import results_mocker