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* Do not install sox system-wide, so that it will never get mixed up with static one torchaudio builds
* Do not install cmake system-wide
* Move libsndfile installation to Docker image

* Use cmake for third party

* Apply patch to libmad

* Update gitignore

* Update docker test image

In #728, linux unit test switches to libsox provided by apt.
For CPU jobs this is fine because all the job steps share the same Docker container,
but on CPU job, each job step runs a script in a new Docker container, so
libsox installed in a step is not available to the subsequent steps.

To fix this, this PR moves the installation of libsox and sox to Docker build.

* Clean up extension build mechanism and extension location

* Add back the switch to depend on external sox

* Remove print

* Fix

* Add GPU test

* Run only on master

* Turn on tests when building through conda-build

* skip one failling test on windows.

* Switch to unittest

* Fix conda env activation

* add linux only condition

* Fix librosa installation

* conda-forge channel as a fallback

* Revert "conda-forge channel as a fallback"

This reverts commit 8c15f6638e34792640a3de3e057d9c2995425180.

* Try the pytorch way

* Use conda-forge

* Disable conda-forge

* Install future at setup env

* Move linux unittest CI job tools to dedicated directory

* Restore Linux scripts and move the updated souces to a new subdir

* Add back future

* Remove comments
Co-authored-by: Vincent Quenneville-Belair <vincentqb@gmail.com>
Co-authored-by: moto <855818+mthrok@users.noreply.github.com>

* Add test image with Kaldi executable and third_parties

* Use Ubuntu as bese image since pytorch/many-linux is huge