Add bisect config validation.

scripts/slave/recipe_modules/auto_bisect/example.py

Index: scripts/slave/recipe_modules/auto_bisect/example.py
diff --git a/scripts/slave/recipe_modules/auto_bisect/example.py b/scripts/slave/recipe_modules/auto_bisect/example.py
index 889dbf5bf2f58b0740195474ebaeabacfbbdf8aa..958497529fc75b1a6e1dafa483a801042ef8ee46 100644
--- a/scripts/slave/recipe_modules/auto_bisect/example.py
+++ b/scripts/slave/recipe_modules/auto_bisect/example.py
@@ -342,15 +342,15 @@ def _get_config(params=None):
       'bad_revision': '314017',
       'metric': 'mean_input_event_latency/mean_input_event_latency',
       'repeat_count': '2',
+      'bug_id': '-1',
       'max_time_minutes': '5',
-      'bug_id': '',
       'gs_bucket': 'chrome-perf',
       'builder_host': 'master4.golo.chromium.org',
       'builder_port': '8341',
       'dummy_builds': 'True',
       'bypass_stats_check': 'True',
       'skip_gclient_ops': 'True',
-      'recipe_tester_name': 'linux_perf_tester'
+      'recipe_tester_name': 'linux_perf_tester',
   }
   if params:
     example_config.update(params)