Setting default username to root and defalut db name to edxapp.

cloudformation_templates/edx-reference-architecture.json

@@ -350,7 +350,7 @@
       "ConstraintDescription":"must be between 1 and 10."
     },
     "DBName":{
-      "Default":"wwc",
+      "Default":"edxapp",
       "Description":"The database name",
       "Type":"String",
       "MinLength":"1",
@@ -359,7 +359,7 @@
       "ConstraintDescription":"must begin with a letter and contain only alphanumeric characters."
     },
     "DBUsername":{
-      "Default":"edxapp",
+      "Default":"root",
       "NoEcho":"true",
       "Description":"The database admin account username",
       "Type":"String",