Map 'shutting-down' node state in EC2 driver to UNKNOWN (previously
mapped to TERMINATED). (LIBCLOUD-280)

Note: This change is backward incompatible which means you need to update
your code if you rely on the old behavior.

Reported by Marcin Kuzminski, part of LIBCLOUD-280.


git-svn-id: https://svn.apache.org/repos/asf/libcloud/trunk@1429656 13f79535-47bb-0310-9956-ffa450edef68