Enable Python deprecation warnings and fix one Boto warning:

  /Users/joshrosen/Documents/spark/ec2/lib/boto-2.34.0/boto/ec2/connection.py:583: PendingDeprecationWarning: The current get_all_instances implementation will be replaced with get_all_reservations.

Quoting from the Boto docs:

    def get_all_instances(self, instance_ids=None, filters=None, dry_run=False,
                          max_results=None):
        """
        Retrieve all the instance reservations associated with your account.

        .. note::
        This method's current behavior is deprecated in favor of
        :meth:`get_all_reservations`.  A future major release will change
        :meth:`get_all_instances` to return a list of
        :class:`boto.ec2.instance.Instance` objects as its name suggests.
        To obtain that behavior today, use :meth:`get_only_instances`.