Add functional tests for add multiple subnets feature

This change adds negative and positive functional tests
for the new feature add multiple subnets per az. Older
functional tests impacted by the feature are fixed. Finally,
the new flags `run_share_server_multiple_subnets_tests` and
`run_network_allocation_update_tests` are added and configured
in the community jobs for Dummy DHSS=True and Container Driver.

Partially-Implements: blueprint multiple-share-network-subnets
Change-Id: I99547e1873646fb1494a454f67b14c7293342beb
diff --git a/zuul.d/manila-tempest-jobs.yaml b/zuul.d/manila-tempest-jobs.yaml
index 494b285..a68aafe 100644
--- a/zuul.d/manila-tempest-jobs.yaml
+++ b/zuul.d/manila-tempest-jobs.yaml
@@ -246,6 +246,8 @@
               backend_names: LONDON,PARIS
               multi_backend: true
               run_share_server_migration_tests: true
+              run_share_server_multiple_subnet_tests: true
+              run_network_allocation_update_tests: true
 
 - job:
     name: manila-tempest-plugin-generic
@@ -490,6 +492,8 @@
               run_replication_tests: true
               run_revert_to_snapshot_tests: true
               run_share_server_migration_tests: true
+              run_share_server_multiple_subnet_tests: true
+              run_network_allocation_update_tests: true
 
 - job:
     name: manila-tempest-plugin-glusterfs-native