Cleanup: Add common "create_server" method

In scenario tests, there are many "create server" methods and their
behaviors are almost same. They creates a server with random name,
default image and default flavor, and waits for server status "ACTIVE".
So this patch adds a common "create_server" method and uses the method
instead of each implementation for code-cleanup.

Change-Id: I663cf1c994307160c9f0ebf51fa4c920f2b6125e
diff --git a/tempest/scenario/test_server_basic_ops.py b/tempest/scenario/test_server_basic_ops.py
index 0ec3a1d..43ac2d9 100644
--- a/tempest/scenario/test_server_basic_ops.py
+++ b/tempest/scenario/test_server_basic_ops.py
@@ -82,26 +82,12 @@
                 self.fail("Failed to create rule in security group.")
 
     def boot_instance(self):
-        i_name = rand_name('instance')
-        flavor_id = self.config.compute.flavor_ref
-        base_image_id = self.config.compute.image_ref
         create_kwargs = {
             'key_name': self.get_resource('keypair').id
         }
-        self.instance = self.compute_client.servers.create(
-            i_name, base_image_id, flavor_id, **create_kwargs)
-        try:
-            self.assertEqual(self.instance.name, i_name)
-            self.set_resource('instance', self.instance)
-        except AttributeError:
-            self.fail("Instance not successfully created.")
-
-        self.assertEqual(self.instance.status, 'BUILD')
-
-    def wait_on_active(self):
-        instance_id = self.get_resource('instance').id
-        self.status_timeout(
-            self.compute_client.servers, instance_id, 'ACTIVE')
+        instance = self.create_server(self.compute_client,
+                                      create_kwargs=create_kwargs)
+        self.set_resource('instance', instance)
 
     def pause_server(self):
         instance = self.get_resource('instance')
@@ -148,7 +134,6 @@
         self.create_keypair()
         self.create_security_group()
         self.boot_instance()
-        self.wait_on_active()
         self.pause_server()
         self.unpause_server()
         self.suspend_server()