When manipulating instance save end states instead of transitional

When starting an instance it should eventually enter running state. At
least in the normal case. So we report pending but save running, this
way when client requests state of instance a second time, we reply with
running.

Similar thing for stop/terminate/reboot.
Implement ImageId parameter in DescribeImages
Implement Elastic IP
Merge pull request #49 from IlyaSukhanov/master

Elastic IP & Instance states