ec2 service: Support VPC and other fixes

AZ was hardcoded if not specified.  This approach doesn't work since not all accounts have the same AZ.  Default AZ is retrieved from AWS if not specified.

Docker-DCO-1.1-Signed-off-by: Aaron Feng aaron.feng@gmail.com (github: aaronfeng)
This is just temporary until we moved everything into subdir structure.