Add gateway in network_info and share network API

Get gateway information from network plugin and put it into network_info.
It is required by EMC Unity storage to create a interface.

APIImpact
DocImpact

Change-Id: I8614b8686af7fa5764b49e8e3cb4a4855dc3a5f4
Implements: blueprint add-gateway-info
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index e2b98a3..7a7ee6f 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -34,7 +34,7 @@
                help="The minimum api microversion is configured to be the "
                     "value of the minimum microversion supported by Manila."),
     cfg.StrOpt("max_api_microversion",
-               default="2.17",
+               default="2.18",
                help="The maximum api microversion is configured to be the "
                     "value of the latest microversion supported by Manila."),
     cfg.StrOpt("region",