Correct neutron docs

The neutron guide refers to ENABLE_PROJECT_VLANS and
PROJECT_VLAN_RANGE but these are not present/checked in the code,
which uses ENABLE_TENANT_VLANS and TENANT_VLAN_RANGE. This
corrects the documentation to match.

Change-Id: I204356c861157e9fab357bb4dde55185bf18a707

Author: edmondsw

doc/source/guides/neutron.rst

@@ -376,8 +376,8 @@ controller node.
 
         ## Neutron options
         Q_USE_SECGROUP=True
-        ENABLE_PROJECT_VLANS=True
-        PROJECT_VLAN_RANGE=3001:4000
+        ENABLE_TENANT_VLANS=True
+        TENANT_VLAN_RANGE=3001:4000
         PHYSICAL_NETWORK=default
         OVS_PHYSICAL_BRIDGE=br-ex