ECS Anywhere install script fixups

[sparrc]

• check curl downloads for failures (404, 403, etc.)
• log what script is doing while waiting for agent to startup
• change wording around agent startup wait
• add license info for ssm agent and docker engine
• a couple shellcheck fixes

Testing

tested on:

• debian
• ubuntu
• sles
• centos

New tests cover the changes:

Description for the changelog

none

Licensing

This contribution is under the terms of the Apache 2.0 License: