Support EC2 instances with no VPC ID. [Ash Wilson]
Uses multi-stage build in Dockerfile to consolidate testing and container image build.
closes #2, closes #4
Changed HALO_API_HOST to HALO_API_HOSTNAME. [Ash Wilson]
This changes the behavior of the tool. HALO_API_HOST was used to define the hostname the SDK used to reach the Halo API. Going forward, users should transition to using HALO_API_HOSTNAME for this.
The default value of api.cloudpassage.com is now set, in the Dockerfile, for HALO_API_HOSTNAME. Any users that currently use this tool against MTG will not need to change anything. Non-MTG users will need to update their container launch environment variables.
Closes #7