Increase opendevzuul-subnet1 from /24 to /20

Since these are not globally routable addresses anyway, we might as
well use a larger network so that we're not constrained by the
subnet size later if we get more than 253 servers worth of quota.

This should be safe since the network is not presently in use for
anything outside of Rackspace Flex, which we haven't hooked up to
Nodepool yet. A cursory search of subset CIDRs also indicates
addresses in this range aren't being configured on virtual
interfaces for existing tests.

Change-Id: Ic32cbc0b24d037c67a5c2f8dd2834013017b8c87

inventory/service/group_vars/bastion.yaml

@@ -126,7 +126,7 @@ cloud_launcher_profiles:
     subnets:
       - name: opendevzuul-subnet1
         network_name: opendevzuul-network1
-        cidr: '10.0.1.0/24'
+        cidr: '10.0.16.0/20'
 
 cloud_launcher_clouds:
   # ovh