Skip test_stamp_pattern until bug 1664793 is fixed

test_stamp_pattern fails for some backends, and
I79ef5b3751747755fc71793f4701e9c886a3e4ff is trying to fix it.

This is to skip test_stamp_pattern until bug 1664793 is fixed.

Change-Id: I79c146f7f5db230097fd30e0ec9f4530337913d6
diff --git a/tempest/scenario/test_stamp_pattern.py b/tempest/scenario/test_stamp_pattern.py
index 8661217..00f892f 100644
--- a/tempest/scenario/test_stamp_pattern.py
+++ b/tempest/scenario/test_stamp_pattern.py
@@ -88,6 +88,7 @@
                                           CONF.compute.build_interval):
             raise lib_exc.TimeoutException
 
+    @decorators.skip_because(bug="1664793")
     @decorators.idempotent_id('10fd234a-515c-41e5-b092-8323060598c5')
     @testtools.skipUnless(CONF.compute_feature_enabled.snapshot,
                           'Snapshotting is not available.')