Javascript Plugin doesn't allow hostname rewrite

[iamdjones]

Branch/Environment/Version

• Branch/Version: master
• Environment: Hybrid

Describe the bug
Javascript Plugins that rewrite hostname get overwritten with upstream configured in the api-def when sending outbound request.

Reproduction steps
Steps to reproduce the behavior:

1. Add custom javascript plugin

var hostnameRewriteMiddleware = new TykJS.TykMiddleware.NewMiddleware({});

hostnameRewriteMiddleware.NewProcessRequest(function(request,session,config){
   
    request.URL = "https://httpbin.org" + request.URL;;

    return hostnameRewriteMiddleware.ReturnData(request, session.meta_data);
});

2. Add api test-api.json
3. Execute curl command "curl http://localhost:5000/test-api"

Actual behavior
The following outbound request (the configured upstream) is executed and returned: http://example.org/

Expected behavior
The following outbound request (with re-written hostname) is executed and returned: https://httpbin.org/

Logs (debug mode or log file):
tyk-gateway.log
Example output from the logs showing "Upstream request URL" with the hostname rewritten by the custom js plugin, and the final "Outbound request URL" with the api-def configured upstream hostname.