Updated configuration and docs for MYSQL_PASSWORD

Updated MYSQL_PASSWORD to DATABASE_PASSWORD in sample
configuration and existing docs

Change-Id: Iafb295a0b7707e08a81e6528620db8543d40f7ae
diff --git a/doc/source/guides/single-machine.rst b/doc/source/guides/single-machine.rst
index 236ece9..a01c368 100644
--- a/doc/source/guides/single-machine.rst
+++ b/doc/source/guides/single-machine.rst
@@ -105,7 +105,7 @@
     FIXED_NETWORK_SIZE=256
     FLAT_INTERFACE=eth0
     ADMIN_PASSWORD=supersecret
-    MYSQL_PASSWORD=iheartdatabases
+    DATABASE_PASSWORD=iheartdatabases
     RABBIT_PASSWORD=flopsymopsy
     SERVICE_PASSWORD=iheartksl
     SERVICE_TOKEN=xyzpdqlazydog