Migrate scenario tests ssh-auth-strategy

Migrate the scenario tests to the new ssh-auth-strategy.

Partially implements: blueprint ssh-auth-strategy

Change-Id: I50759d32e47d975ec64ca129a13b2ae4459917e4
diff --git a/tempest/scenario/test_snapshot_pattern.py b/tempest/scenario/test_snapshot_pattern.py
index cd59334..f3b6558 100644
--- a/tempest/scenario/test_snapshot_pattern.py
+++ b/tempest/scenario/test_snapshot_pattern.py
@@ -36,14 +36,6 @@
 
     """
 
-    def _boot_image(self, image_id, keypair, security_group):
-        security_groups = [{'name': security_group['name']}]
-        create_kwargs = {
-            'key_name': keypair['name'],
-            'security_groups': security_groups
-        }
-        return self.create_server(image=image_id, create_kwargs=create_kwargs)
-
     @test.idempotent_id('608e604b-1d63-4a82-8e3e-91bc665c90b4')
     @testtools.skipUnless(CONF.compute_feature_enabled.snapshot,
                           'Snapshotting is not available.')
@@ -54,8 +46,12 @@
         security_group = self._create_security_group()
 
         # boot an instance and create a timestamp file in it
-        server = self._boot_image(CONF.compute.image_ref, keypair,
-                                  security_group)
+        server = self.create_server(
+            image_id=CONF.compute.image_ref,
+            key_name=keypair['name'],
+            security_groups=[{'name': security_group['name']}],
+            wait_until='ACTIVE')
+
         instance_ip = self.get_server_or_ip(server)
         timestamp = self.create_timestamp(instance_ip,
                                           private_key=keypair['private_key'])
@@ -64,8 +60,11 @@
         snapshot_image = self.create_server_snapshot(server=server)
 
         # boot a second instance from the snapshot
-        server_from_snapshot = self._boot_image(snapshot_image['id'],
-                                                keypair, security_group)
+        server_from_snapshot = self.create_server(
+            image_id=snapshot_image['id'],
+            key_name=keypair['name'],
+            security_groups=[{'name': security_group['name']}],
+            wait_until='ACTIVE')
 
         # check the existence of the timestamp file in the second instance
         server_from_snapshot_ip = self.get_server_or_ip(server_from_snapshot)