Add UUIDs to all tempest tests and gate check

Adds uuid4 as a decorator of the form:
@test.idempotent_id('12345678-1234-1234-1234-123456789abc')
to every test in the Tempest tree. Includes a gate check to
ensure the existence and uniqueness of the ids.

Modify check tool to ignore Tempest unit tests.

Change-Id: I19e3c7dd555a3ea09d585fb9091c357a300e6559
Co-Authored-By: Sergey Slipushenko <sslypushenko@mirantis.com>
Implements: bp test-uuid
diff --git a/tempest/scenario/test_snapshot_pattern.py b/tempest/scenario/test_snapshot_pattern.py
index 5cb7c99..109d36b 100644
--- a/tempest/scenario/test_snapshot_pattern.py
+++ b/tempest/scenario/test_snapshot_pattern.py
@@ -57,6 +57,7 @@
         got_timestamp = ssh_client.exec_command('cat /tmp/timestamp')
         self.assertEqual(self.timestamp, got_timestamp)
 
+    @test.idempotent_id('608e604b-1d63-4a82-8e3e-91bc665c90b4')
     @testtools.skipUnless(CONF.compute_feature_enabled.snapshot,
                           'Snapshotting is not available.')
     @test.services('compute', 'network', 'image')