Migrated 2 network clients from tempest

This migrates the above files from tempest.
This includes tempest commits:

 * security_group_rules_client.py: I2cd6bef13a16672bf0dbf6aeab0c60f0221e1a49
 * extensions_client.py          : I49b30eac4d7db0b06a3b0946158e542801cf4e75

to see the commit history for these files refer to the above Change-Ids
in the tempest repository.

Partially implements blueprint migrate-service-clients-to-tempest-lib

Change-Id: I76b1d0b1c3ffb2c366c4e6d95105d9c8fde2a22b

tempest_lib/services/network/extensions_client.py

@@ -0,0 +1,24 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from tempest_lib.services.network import base
+
+
+class ExtensionsClient(base.BaseNetworkClient):
+
+    def show_extension(self, ext_alias, **fields):
+        uri = '/extensions/%s' % ext_alias
+        return self.show_resource(uri, **fields)
+
+    def list_extensions(self, **filters):
+        uri = '/extensions'
+        return self.list_resources(uri, **filters)

tempest_lib/services/network/security_group_rules_client.py

@@ -0,0 +1,33 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from tempest_lib.services.network import base
+
+
+class SecurityGroupRulesClient(base.BaseNetworkClient):
+
+    def create_security_group_rule(self, **kwargs):
+        uri = '/security-group-rules'
+        post_data = {'security_group_rule': kwargs}
+        return self.create_resource(uri, post_data)
+
+    def show_security_group_rule(self, security_group_rule_id, **fields):
+        uri = '/security-group-rules/%s' % security_group_rule_id
+        return self.show_resource(uri, **fields)
+
+    def delete_security_group_rule(self, security_group_rule_id):
+        uri = '/security-group-rules/%s' % security_group_rule_id
+        return self.delete_resource(uri)
+
+    def list_security_group_rules(self, **filters):
+        uri = '/security-group-rules'
+        return self.list_resources(uri, **filters)