Add a better redis health check that reads and writes

This will hopefully catch issues earlier with Redis

data/buildlogs.py

@@ -1,5 +1,6 @@
 import redis
 import json
+import time
 
 from util.dynamic import import_class
 from datetime import timedelta
@@ -65,7 +66,6 @@ class RedisBuildLogs(object):
     """
     self._redis.expire(self._logs_key(build_id), ONE_DAY)
 
-
   @staticmethod
   def _status_key(build_id):
     return 'builds/%s/status' % build_id
@@ -88,9 +88,20 @@ class RedisBuildLogs(object):
 
     return json.loads(fetched) if fetched else None
 
+  @staticmethod
+  def _health_key():
+    return '_health'
+
   def check_health(self):
     try:
-      return self._redis.ping() == True
+      if not self._redis.ping() == True:
+        return False
+
+      # Ensure we can write and read a key.
+      self._redis.set(self._health_key(), time.time())
+      self._redis.get(self._health_key())
+
+      return True
     except redis.ConnectionError:
       return False