Infect EC2Connection object
Inject userdata by base64 encoding
If Name tag is None, use ec2 id as EBS tag prefix
Revise behavior when setting "wait_until_running"

* Not use instance.state
* Instead of above, use following two statuses
    + InstanceStatus.instance_status.status
    + InstanceStatus.system_status.status
Add Elastic nic options.
Implement associate_public_ip
Set base image id when excute set_base_image()
Tweak output indent when setting dry-run
Enable instance termination protect option
Write some tests

* Modify nic options
* Move modifing security group and subnet id to nic from ec2
tweak align flake8 style