* auth/aws: Allow binding by EC2 instance IDs
This allows specifying a list of EC2 instance IDs that are allowed to
bind to the role. To keep style formatting with the other bindings, this
is still called bound_ec2_instance_id rather than bound_ec2_instance_ids
as I intend to convert the other bindings to accept lists as well (where
it makes sense) and keeping them with singular names would be the
easiest for backwards compatibility.
Partially fixes#3797
39dc981301