Added a failing test for ``nextToken`` in ``InstanceStatusSet``.
fix typo in xml parsing for InstanceStatusSet

The correct XML element name is 'nextToken', not 'NextToken'. (http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeInstanceStatus.html)
Merge branch 'ec2-instancestatus-nexttoken' into develop