Moving the $wp_http_api_test inside management_page function

After moving the add_management_page function to a callback, the plugin was working except the ajax script was not executing.

To fix this I also moved the global $wp_http_api_test declaration from the construct to
the management_page() call back.

The ajax script was not executing do the the conditional return located
in scripts($hook) function.

Attached is a screenshot of the plugin functioning properly with response data

![capture-wp-http-api-tester](https://f.cloud.github.com/assets/5017299/805922/ca4b9a8e-ee2f-11e2-9a58-322f3631e4bd.PNG)