rpc_interface: add get_db_test rpc

get_db_test does a quick db connection, and returns ether 'Success' or
'Failure'

BUG=chromium:715386
TEST=./rpc_interface_unittest.py

Change-Id: I9e2cd553369ff39d26a21b640d655584878db648
Reviewed-on: https://chromium-review.googlesource.com/537213
Commit-Ready: Chris Ching <[email protected]>
Tested-by: Chris Ching <[email protected]>
Reviewed-by: Prathmesh Prabhu <[email protected]>
diff --git a/frontend/afe/rpc_interface_unittest.py b/frontend/afe/rpc_interface_unittest.py
index 8ff9cbd..635c7f1 100755
--- a/frontend/afe/rpc_interface_unittest.py
+++ b/frontend/afe/rpc_interface_unittest.py
@@ -73,6 +73,10 @@
                           set(expected_hostnames))
 
 
+    def test_ping_db(self):
+        self.assertEquals(rpc_interface.ping_db(), [True])
+
+
     def test_get_hosts(self):
         hosts = rpc_interface.get_hosts()
         self._check_hostnames(hosts, [host.hostname for host in self.hosts])