ganeti.http: Add constant for DELETE

Reviewed-by: amishchenko

lib/http/__init__.py

@@ -52,6 +52,7 @@ HTTP_GET = "GET"
 HTTP_HEAD = "HEAD"
 HTTP_POST = "POST"
 HTTP_PUT = "PUT"
+HTTP_DELETE = "DELETE"
 
 HTTP_ETAG = "ETag"
 HTTP_HOST = "Host"