Include timezone in timestamp fields

The Neutron 'created_at'/'updated_at' fields on API resources
were inconsistent with other OpenStack projects because we did
not include timezone information. This patch addressed that
problem by adding the zulu time indicator onto the end of the
fields.

Because this could break clients expecting no timezone, this patch
also eliminates the 'timestamp_core' and 'timestamp_ext' extensions
and consolidates them into a new 'timestamp' extension. This makes
the change discoverable via the API.

This is assuming the current API development paradigm where
extensions can come and go depending on the deployment and the client
is expected to handle this by checking the loaded extensions.
Once we decide extensions are permanent, this type of change will
no longer be possible.

Even though this is being proposed late in the cycle, it is better
to get this change in before the release where we expose even more
resources with incorrectly formatted timestamps.

APIImpact
Closes-Bug: #1561200
Change-Id: I2ee2ed4c713d88345adc55b022feb95653eec663
diff --git a/neutron/tests/tempest/api/test_timestamp.py b/neutron/tests/tempest/api/test_timestamp.py
index 290e162..d3a2361 100644
--- a/neutron/tests/tempest/api/test_timestamp.py
+++ b/neutron/tests/tempest/api/test_timestamp.py
@@ -34,7 +34,7 @@
     larger_prefix = '10.11.0.0/16'
 
     @classmethod
-    @test.requires_ext(extension="timestamp_core", service="network")
+    @test.requires_ext(extension="standard-attr-timestamp", service="network")
     def skip_checks(cls):
         super(TestTimeStamp, cls).skip_checks()
 
@@ -186,8 +186,9 @@
     def skip_checks(cls):
         super(TestTimeStampWithL3, cls).skip_checks()
 
-        if not test.is_extension_enabled('timestamp_ext', 'network'):
-            raise cls.skipException("timestamp_ext extension not enabled")
+        if not test.is_extension_enabled('standard-attr-timestamp', 'network'):
+            raise cls.skipException("standard-attr-timestamp extension not "
+                                    "enabled")
 
     @classmethod
     def resource_setup(cls):
@@ -260,8 +261,9 @@
     def skip_checks(cls):
         super(TestTimeStampWithSecurityGroup, cls).skip_checks()
 
-        if not test.is_extension_enabled('timestamp_ext', 'network'):
-            raise cls.skipException("timestamp_ext extension not enabled")
+        if not test.is_extension_enabled('standard-attr-timestamp', 'network'):
+            raise cls.skipException("standard-attr-timestamp extension not "
+                                    "enabled")
 
     @classmethod
     def resource_setup(cls):