Toggle on/off ffmpeg test if needed (#2901)

Summary:
Toggle on/off ffmpeg test if needed
By default it ON, hence should not affect any current tests.
To toggle ON no change required.
To toggle OFF use:
```
smoke_test.py --no-ffmpeg
```

To be used when calling from builder currently. Since we do not install ffmpeg currently.

Pull Request resolved: https://github.com/pytorch/audio/pull/2901

Reviewed By: carolineechen, mthrok

Differential Revision: D41874976

Pulled By: atalman

fbshipit-source-id: c57b19f37c63a1f476f93a5211550e980e67d9c7

test/smoke_test/smoke_test.py

 """Run smoke tests"""
 
+import argparse
+
 import torchaudio  # noqa: F401
 import torchaudio.compliance.kaldi  # noqa: F401
 import torchaudio.datasets  # noqa: F401
@@ -9,4 +11,22 @@ import torchaudio.pipelines  # noqa: F401
 import torchaudio.sox_effects  # noqa: F401
 import torchaudio.transforms  # noqa: F401
 import torchaudio.utils  # noqa: F401
-from torchaudio.io import StreamReader  # noqa: F401
+
+
+def ffmpeg_test():
+    from torchaudio.io import StreamReader  # noqa: F401
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+
+    # Warning: Please note this option should not be widely used, only use it when absolutely necessary
+    parser.add_argument("--no-ffmpeg", dest="ffmpeg", action="store_false")
+
+    options = parser.parse_args()
+    if options.ffmpeg:
+        ffmpeg_test()
+
+
+if __name__ == "__main__":
+    main()