Conditionally mark test_attach_detach_volume as slow

Based on average test times from the last 300 runs
of the tempest-full job [1] this change marks the
test_attach_detach_volume test as slow but only if
SSH validation is enabled, which it is in tempest-full
but might not be in other jobs that run it, for example
in refstack which uses this test for interoperability
certification.

[1] http://paste.openstack.org/show/745114/

Change-Id: I47710321d8dfb0345c793e66bd09a5dd1933557b
Related-Bug: #1783405
diff --git a/tempest/api/compute/volumes/test_attach_volume.py b/tempest/api/compute/volumes/test_attach_volume.py
index f7b5b4b..8bb4eaa 100644
--- a/tempest/api/compute/volumes/test_attach_volume.py
+++ b/tempest/api/compute/volumes/test_attach_volume.py
@@ -65,6 +65,8 @@
 class AttachVolumeTestJSON(BaseAttachVolumeTest):
 
     @decorators.idempotent_id('52e9045a-e90d-4c0d-9087-79d657faffff')
+    # This test is conditionally marked slow if SSH validation is enabled.
+    @decorators.attr(type='slow', condition=CONF.validation.run_validation)
     def test_attach_detach_volume(self):
         # Stop and Start a server with an attached volume, ensuring that
         # the volume remains attached.