Add --xfvb and --jobs=1 args for linux-tcmalloc-rel bot.

Re-run testing/buildbot/generate_buildbot_json.py

BUG=868024

Change-Id: Iae857082985de453d256150f2ef653f9f570337f
Reviewed-on: https://chromium-review.googlesource.com/c/1286757
Commit-Queue: Will Harris <wfh@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600772}

testing/buildbot/chromium.fyi.json

@@ -6379,6 +6379,10 @@
         }
       },
       {
+        "args": [
+          "--xvfb",
+          "--jobs=1"
+        ],
         "isolate_name": "telemetry_perf_unittests",
         "name": "telemetry_perf_unittests",
         "swarming": {

testing/buildbot/test_suite_exceptions.pyl

@@ -1127,6 +1127,13 @@
         },
         'experiment_percentage': 100,
       },
+      # luci.chromium.ci
+      'linux-tcmalloc-rel': {
+        'args': [
+          '--xvfb',
+          '--jobs=1',
+        ],
+      },
     },
     'remove_from': [
       'Linux Tests (dbg)(1)(32)',