Collect and report last reconfigured timestamp

* ms timestamp collected each time Scheduler.reconfigure() completed
* last reconfigured timestamp reported through the status.json
* it could be useful to determine when zuul conf reloaded

Change-Id: I03c5a5734f2127ef40be9ec512c983b136508be7
diff --git a/etc/status/public_html/status-basic.json-sample b/etc/status/public_html/status-basic.json-sample
index 4e12cd6..9ee6d25 100644
--- a/etc/status/public_html/status-basic.json-sample
+++ b/etc/status/public_html/status-basic.json-sample
@@ -1,4 +1,5 @@
 {
+    "last_reconfigured": 1389381756000,
     "message": "Example error message",
     "pipelines": [
         {