active_merchant: allow user to pass custom properties in killbill_spec_helper

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
active_merchant: fix private_payment_plugin

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
spec: add test for StreamyResultSet

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
utils: add utilities to retrieve the host IP address

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
active_merchant: let user override the linked transaction type

Depending on the gateway, captures and refunds can be applied on
different object types (original authorization, last capture, etc.).
Keep the same default but let the user override it if needed.

This also adds some convenience methods in models.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
active_merchant: simplify private_api constructor

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
active_merchant: fix typos

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>