util: json: Fix freeing of objects appended to virJSONValue

util: json: Fix freeing of objects appended to virJSONValue

It was not possible to determine whether virJSONValueObjectAddVArgs and
the functions using it would consume a virJSONValue or not when used
with the 'a' or 'A' modifier depending on when the loop failed.

Fix this by passing in a pointer to the pointer so that it can be
cleared once it's successfully consumed and the callers don't have to
second-guess leaving a chance of leaking or double freeing the value
depending on the ordering.

Fix all callers to pass a double pointer too.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>