Correct mispell words in comments

1) test_list_hosts_with_nonexistent_zone
   "and no hosts will be retured", "retured"
2) test_update_default_quotas
   "that we go from -1 (unlimitted)", "unlimitted"
...
and so on

Change-Id: I185a792e03f78d34dff4a923d0f34902470497ce
Closes-Bug: #1578930
diff --git a/tempest/lib/cmd/skip_tracker.py b/tempest/lib/cmd/skip_tracker.py
index b7d6a24..f35b14c 100755
--- a/tempest/lib/cmd/skip_tracker.py
+++ b/tempest/lib/cmd/skip_tracker.py
@@ -48,7 +48,7 @@
 
 
 def find_skips(start):
-    """Find the entire list of skiped tests.
+    """Find the entire list of skipped tests.
 
     Returns a list of tuples (method, bug) that represent
     test methods that have been decorated to skip because of