Eucalyptus support

Hey Team,

Ive created the plugins necessary to use Aminator with a Eucalyptus cloud with KVM as the hypervisor and Virtio device drivers. Please let me know how I can improve the implementation. 

The syntax is as follows:
```
 aminate -e euca_apt_linux --ec2-endpoint 10.0.1.91 --name "Web Server" -B emi-B4143CA4 apache2
```
Where "--ec2-endpoint" is the hostname or IP of the Eucalyptus Cloud Controller. The following environments were added:
 - euca_apt_linux
 - euca_yum_linux
 - euca_apt_script_linux