The default transport for the VI API is HTTPS. If the server redirects
from HTTPS to HTTP the driver would silently follow that redirection.
The user assumes to communicate with the server over a secure transport
but isn't.

This patch disables automatical redirection following. The driver reports
an error if the server tries to redirect.

* src/esx/esx_vi.c: refactor the call to curl_easy_perform() into a
  function and do error handling there, disable automatical redirection
  following for curl
* src/esx/esx_vi.h: change the type of responseCode to int