Deprecate swift3, use s3api in Swift repo

swift3 is no longer actively maintained in the upstream.
That has been moved to Swift repository as s3api so we should
use s3api middleware instead. As well as swift3, s3token is
also maintained in Swift upstream.

Change-Id: I4582d81da066ab53e6f11ad1df7af91425f2b0ca
diff --git a/lib/nova b/lib/nova
index 1fb50df..4653d69 100644
--- a/lib/nova
+++ b/lib/nova
@@ -403,7 +403,7 @@
     fi
 
     # S3
-    if is_service_enabled swift3; then
+    if is_service_enabled s3api; then
         get_or_create_service "s3" "s3" "S3"
         get_or_create_endpoint \
             "s3" \