Fix misspellings in tempest

Fix misspellings detected by:
* pip install misspellings
* git ls-files | grep -v locale | misspellings -f -

Change-Id: Ib92aabf48a18a32aa7384f7ad4b7337be78edc34
Closes-Bug: #1257295
diff --git a/tempest/common/waiters.py b/tempest/common/waiters.py
index dbeba8f..8e6b9fb 100644
--- a/tempest/common/waiters.py
+++ b/tempest/common/waiters.py
@@ -42,7 +42,7 @@
     timeout = client.build_timeout + extra_timeout
     while True:
         # NOTE(afazekas): Now the BUILD status only reached
-        # between the UNKOWN->ACTIVE transition.
+        # between the UNKNOWN->ACTIVE transition.
         # TODO(afazekas): enumerate and validate the stable status set
         if status == 'BUILD' and server_status != 'UNKNOWN':
             return