ci: Separate pipeline for tensorflow-enabled linux builds

[jailuthra]

What does this pull request do? Explain your changes. (required)

Separate out the build process when libtensorflow is enabled.

Specific updates (required)

see commit history

How did you test each of these updates (required)

The CI builds + uploads work as expected.
https://build.livepeer.live/0.5.18-3aa0d8ca/livepeer-linux-tensorflow-amd64.tar.gz <-- Depends on libtensorflow.so - ldd livepeer | grep tensorflow
https://build.livepeer.live/0.5.18-3aa0d8ca/livepeer-linux-amd64.tar.gz <-- Standard build with no runtime dependency
Does this pull request close any open issues?

Fixes #1919

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[yondonfu]

Summary of my current understanding of the CI process:

• Linux
  • Tensorflow Build
    • Always enables Tensorflow. User will need to download libtensorflow themselves to use with the binary
    • Only enables scene classification capability for non-semver tagged releases
  • Regular Build
    • Never enables Tensorflow
    • Only enables scene classification capability for non-semver tagged releases
    • Since Tensorflow is never enabled, scene classification can be enabled for a non-semver tagged release, but will not actually work
• Docker
  • Always enables Tensorflow and libtensorflow is included in the image
  • Only enables scene classification capability for non-semver tagged releases
• Windows
  • Never enables Tensorflow
  • Only enables scene classification capability for non-semver tagged releases
  • Since Tensorflow is never enabled, scene classification can be enabled for a non-semver tagged release, but will not actually work
• Darwin
  • Never enables Tensorflow
  • Only enables scene classification capability for non-semver tagged releases
  • Since Tensorflow is never enabled, scene classification can be enabled for a non-semver tagged release, but will not actually work

[yondonfu]

Just want to make sure we're on the same page about this comment.

Other than that LGTM after squashing.

[jailuthra]

Summary of my current understanding of the CI process:
..

Thanks for the summary, and yeah that sounds about right!
Keeping it functional only for linux + non-semver because the usecase (for now) is limited to our deployments and not to the wider community.