Use Subnet pools to avoid cidr concurrency issues

This patch removes the tobiko.openstack.neutron._cidr module that was
used to generate CIDRs whenever tobiko was going to create a new subnet.
That method had problems when several tobiko workers running in parallel
tried to create subnets. Collisions happened sometimes, resulting in the
creation of two subnets with a common CIDR that could fail if they were
connected to a common router.

This patch uses the neutron subnet pool feature [1]. When Tobiko creates
a subnet, it will not calculate a free IPv4/IPv6 CIDR, but will
associate that subnet to common Subnet Pools, shared by the different
tests. When the subnet is created, it is neutron responsibiltiy to
allocate a free CIDR for that subnet, based on the created Subnet Pools.

The method that creates the Subnet Pools uses an
@oslo_concurrency.lockutils.synchronized decorator to guarantee that two
Tobiko workers do not create the same Subnet Pool at the same time.

[1] https://docs.openstack.org/neutron/latest/admin/config-subnet-pools.html

Change-Id: I3b09e468310e06f8c4b7d7dbec02e4b2e6f67530

tobiko/openstack/stacks/neutron/network.yaml

@@ -27,17 +27,13 @@ parameters:
     type: boolean
     default: false
 
-  ipv4_cidr:
-    description: IPv4 subnet CIDR to be assigned to new network
+  subnet_pool_ipv4_id:
+    description: IPv4 Subnet Pool ID
     type: string
-    constraints:
-      - custom_constraint: net_cidr
 
-  ipv6_cidr:
-    description: IPv6 subnet CIDR to be assigned to new network
+  subnet_pool_ipv6_id:
+    description: IPv6 Subnet Pool ID
     type: string
-    constraints:
-      - custom_constraint: net_cidr
 
   ipv4_dns_nameservers:
     description: IPv4 nameservers IP addresses
@@ -125,7 +121,7 @@ resources:
     properties:
       network: {get_resource: _network}
       ip_version: 4
-      cidr: {get_param: ipv4_cidr}
+      subnetpool: {get_param: subnet_pool_ipv4_id}
       dns_nameservers: {get_param: ipv4_dns_nameservers}
 
   _ipv6_subnet:
@@ -134,7 +130,7 @@ resources:
     properties:
       network: {get_resource: _network}
       ip_version: 6
-      cidr: {get_param: ipv6_cidr}
+      subnetpool: {get_param: subnet_pool_ipv6_id}
       dns_nameservers: {get_param: ipv6_dns_nameservers}
       ipv6_address_mode: {get_param: ipv6_address_mode}
       ipv6_ra_mode: {get_param: ipv6_ra_mode}