Prepare RNNT to switch to Numba loss for compatibility
This pull request **fixes 2 alerts** when merging 4848e4c0e5059d4a31262dcd7c5ba54c077f2691 into 094b58bfcefd069aad930a375f7a93fd26af45a2 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-5012310c004b9db9ea2d601621c420f3c4619363)

**fixed alerts:**

* 2 for Unused import This pull request **fixes 2 alerts** when merging 0d2c04146e472b4714e2c727ec0f201afc252940 into 094b58bfcefd069aad930a375f7a93fd26af45a2 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-07a31dca89da3bde05f3506bc01ef5ea88fd6c7d)

**fixed alerts:**

* 2 for Unused import This pull request **fixes 2 alerts** when merging b281d1f1f6e1fac7c6dfe71f6bd43d7712da6fe6 into 682e90d5ab1085ba07e520dec42cc60d362d4aca - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-8b570105ba7c3be4838c95b6386f78d53201d8e4)

**fixed alerts:**

* 2 for Unused import
# Changelog
- Add rnnt loss switching capability.
- Enable passing arbitrary kwargs to the inner loss function.
- Add jenkins tests (commented out until 21.04 container is released which supports minimum numba version 0.53 for CUDA 11.2)
- Enable all RNNT model tests using the numba default loss

Signed-off-by: smajumdar <titu1994@gmail.com>