Fix typos
replace seperate with separate

Change-Id: I22b0e9d889a507107e853777ec6cfa56fb93d7aa
diff --git a/tempest/cmd/run.py b/tempest/cmd/run.py
index 72ee715..a27425c 100644
--- a/tempest/cmd/run.py
+++ b/tempest/cmd/run.py
@@ -244,7 +244,7 @@
                                  'each newline')
         parser.add_argument('--load-list', '--load_list',
                             help='Path to a non-regex whitelist file, '
-                                 'this file contains a seperate test '
+                                 'this file contains a separate test '
                                  'on each newline. This command'
                                  'supports files created by the tempest'
                                  'run ``--list-tests`` command')