Adjust API tests for NotImplemented skip

This is a patch to restructure the API tests to use the
new skip_if_not_implemented capability.

Depends-On: https://review.opendev.org/745239

Change-Id: I291488e1c9418e51d6fe7ea142eaca13e3c181a0
diff --git a/octavia_tempest_plugin/common/constants.py b/octavia_tempest_plugin/common/constants.py
index ee4c16a..3bf8f3c 100644
--- a/octavia_tempest_plugin/common/constants.py
+++ b/octavia_tempest_plugin/common/constants.py
@@ -57,6 +57,7 @@
 INSERT_HEADERS = 'insert_headers'
 X_FORWARDED_FOR = 'X-Forwarded-For'
 X_FORWARDED_PORT = 'X-Forwarded-Port'
+X_FORWARDED_PROTO = 'X-Forwarded-Proto'
 TAGS = 'tags'
 TIMEOUT_CLIENT_DATA = 'timeout_client_data'
 TIMEOUT_MEMBER_CONNECT = 'timeout_member_connect'