web: add /{tenant}/builds route

This change adds a SqlHandler to query the sql reporter database from
zuul-web through the /{tenant}/builds.json controller.

This change also adds a /{tenant}/builds.html basic web interface.

Change-Id: I423a37365316cc96ed07ad0895c7198d9cff8be5
diff --git a/etc/zuul.conf-sample b/etc/zuul.conf-sample
index f0e1765..17092af 100644
--- a/etc/zuul.conf-sample
+++ b/etc/zuul.conf-sample
@@ -38,6 +38,7 @@
 listen_address=127.0.0.1
 port=9000
 static_cache_expiry=0
+;sql_connection_name=mydatabase
 
 [webapp]
 listen_address=0.0.0.0