host-containers: default "enabled" and "superpowered" to false

[etungsten]

Issue number:
Partially addresses #1385

Description of changes:

Author: Erikson Tung <etung@amazon.com>
Date:   Mon May 17 16:37:52 2021 -0700

    host-containers: default "enabled" and "superpowered" to false
    
    Defaults "enabled" and "superpowered" to false when not defined.

Testing done:
Launched instance with the following userdata.
self-terminator doesn't have either enabled or superpowered specified

[settings.host-containers.admin]
enabled = true

[settings.host-containers.control]
enabled = true

[settings.host-containers.self-terminator]
source="snip.dkr.ecr.us-west-2.amazonaws.com/self-terminator:latest"

The host was able to come up fine and the settings are as expected:

   "host-containers":{
      ...,
      "self-terminator":{
         "source":"snip.dkr.ecr.us-west-2.amazonaws.com/self-terminator:latest"
      }
   },

Then checking the host-container's environment variables, both enabled and superpowered are defaulted to false.

bash-5.0# cat /etc/host-containers/self-terminator.env 
CTR_SUPERPOWERED=false
CTR_SOURCE=snip.dkr.ecr.us-west-2.amazonaws.com/self-terminator:latest

# Just for reference; service is enabled or disabled by host-containers service
# CTR_ENABLED=false

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.