compute: Move device tagging tests to use wait_until=SSHABLE

Waiting until the test instance is SSH-able before continuing
the test will help us avoid failures to detach a volume from
server, more info in the related bug.

Related-Bug: #1960346

Change-Id: Id5496572ce6cef06e71bae1a1040b274bacf4f79
diff --git a/tempest/api/compute/servers/test_device_tagging.py b/tempest/api/compute/servers/test_device_tagging.py
index f5c9080..d099fce 100644
--- a/tempest/api/compute/servers/test_device_tagging.py
+++ b/tempest/api/compute/servers/test_device_tagging.py
@@ -212,7 +212,7 @@
 
         server = self.create_test_server(
             validatable=True,
-            wait_until='ACTIVE',
+            wait_until='SSHABLE',
             validation_resources=validation_resources,
             config_drive=config_drive_enabled,
             name=data_utils.rand_name('device-tagging-server'),