Added the ability to add volumes to instances at creation time

This allows a volume to be cloned from a snapshot, a brand new
volume to be created, or an ephemeral volumes to be associated
at time of instance creation.

This avoids any race conditions associated with creating extra volumes
after instance creation (e.g. writes happening before the volume is
mounted).

In addition, this allows the root volume to be edited
Merge pull request #4534 from willthames/ec2_mount_volumes

Added the ability to add EBS volumes to EC2 instances at creation time