[testing] use xenial for some swarming test

TBR=jbudorick

Bug: 954450
Change-Id: Id3873fb74eca4c71929f9db96e78b6bb87e1b51c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1686696
Reviewed-by: Takuto Ikuta <[email protected]>
Commit-Queue: Takuto Ikuta <[email protected]>
Auto-Submit: Takuto Ikuta <[email protected]>
Cr-Commit-Position: refs/heads/master@{#675535}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index 50cf586..cf8f0f0 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -516,7 +516,7 @@
             {
               'device_os': None,
               'device_type': None,
-              'os': 'Ubuntu-14.04',
+              'os': 'Ubuntu-16.04',
             },
           ],
         },
@@ -1861,7 +1861,7 @@
         'swarming': {
           'dimension_sets': [
             {
-              'os': 'Ubuntu-14.04',
+              'os': 'Ubuntu-16.04',
             },
           ],
           'shards': 20,
@@ -1878,7 +1878,7 @@
         'swarming': {
           'dimension_sets': [
             {
-              'os': 'Ubuntu-14.04',
+              'os': 'Ubuntu-16.04',
             },
           ],
           'shards': 10,