Make version generation consistent across build targets

[fierlion]

Summary

Update each of the build processes to use the build-time version rather than the existing version. Also removing the * in our path, but not from the human-readable string.

Implementation details

Update build-integrated to use the buildroot for version file update; update each make target/script/spec file to use the version_gen=true path in build-integrated.

also note that this reverts a workaround in our builds 6e8c9a5

Testing

Tested on AL2 instance
Added a fresh commit then built for each of the following targets to be sure I was picking up the latest:

make dockerfree-agent-image
make generic-rpm-integrated
make amazon-linux-rpm-integrated

also checked that make generic-deb-integrated works, as it calls make dockerfree-agent-image to build the agent.
And also note that I tested the koji-built agent and it is consistent already so no work required there:
https://github.com/aws/amazon-ecs-agent/releases/tag/v1.66.2 <- 06008fa
in the koji-built agent:

"Version": "Amazon ECS Agent - v1.66.2 (06008fa1)"

New tests cover the changes: no

Description for the changelog

Fix agent short hash version bug

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[sparrc]

how was this working before if ecs-init.spec doesn't exist?

[fierlion]

actually that's a good point -- this was working because koji doesn't actually use this Makefile so this target is more a reference to approximate what koji builds rather than the mechanism koji uses to build.