func_curl: Add 'followlocation' option to CURLOPT()

We allow for 'maxredirs' to be set, but this value is ignored when
followlocation is not enabled which, by default, it is not.

ASTERISK-17491 #close
Reported by: candrews

Change-Id: I96a4ab0142f2fb7d2e96ff976f6cf7b2982c761a