Eliminate the impact of "wait_until='BUILD'"

BUILD is just a middle state within a short period of time.
It's suspended and unstable when creating a server,
and it will be ACTIVE eventually if everything is ok.

But many places uses the wait_until='BUILD' to create server.
resp, server = cls.create_server(image_id=cls.image_ref,
                                   flavor=cls.flavor_ref,
                                   wait_until='BUILD')

In this patch I add following code in wait_for_server_status
method instead of deleting those incorrect usage.
Thus will use the smallest change
to support BUILD state for wait_until as well.

if status == 'BUILD' and server_status != 'UNKNOWN':
            return

Change-Id: I146fdff56af29ae0aef9b5cff8bcea5468ff595c
Closes-Bug: #1214202
diff --git a/tempest/services/compute/json/servers_client.py b/tempest/services/compute/json/servers_client.py
index 6906610..c5827f6 100644
--- a/tempest/services/compute/json/servers_client.py
+++ b/tempest/services/compute/json/servers_client.py
@@ -157,6 +157,8 @@
         start = int(time.time())
 
         while(server_status != status):
+            if status == 'BUILD' and server_status != 'UNKNOWN':
+                return
             time.sleep(self.build_interval)
             resp, body = self.get_server(server_id)
             server_status = body['status']
diff --git a/tempest/services/compute/xml/servers_client.py b/tempest/services/compute/xml/servers_client.py
index 5c7a629..ec9464a 100644
--- a/tempest/services/compute/xml/servers_client.py
+++ b/tempest/services/compute/xml/servers_client.py
@@ -312,6 +312,8 @@
         start = int(time.time())
 
         while(server_status != status):
+            if status == 'BUILD' and server_status != 'UNKNOWN':
+                return
             time.sleep(self.build_interval)
             resp, body = self.get_server(server_id)
             server_status = body['status']