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/manila_tempest_tests/utils.py b/manila_tempest_tests/utils.py
index d0860f0..5ecfb36 100644
--- a/manila_tempest_tests/utils.py
+++ b/manila_tempest_tests/utils.py
@@ -94,6 +94,16 @@
     return lambda f: f
 
 
+def skip_if_is_microversion_ge(left, right):
+    """Skip if version for left is greater than or equal to the right one."""
+
+    if is_microversion_ge(left, right):
+        reason = ("Skipped. Test requires microversion "
+                  "< than '%s'." % right)
+        return testtools.skip(reason)
+    return lambda f: f
+
+
 def check_skip_if_microversion_not_supported(microversion):
     """Callable method for tests that are microversion-specific."""
     if not is_microversion_supported(microversion):