Retrieve EC2 state when using newer versions of Boto

In https://github.com/boto/boto/commit/a23c379837f698212252720d2af8dec0325c9518, Boto changed how it stores state/state_code from attributes on an instance to properties, which aren't automatically picked up as host vars by the inventory script.

This change adds support for state, state_code, previous_state, and previous_state_code host vars when using newer versions of Boto, and should still work for older versions as before.