Add some improvements for pipeline module, engine and assertion into ds engine

[hyunwoongko]

There are some improvements.

1. Improve error message of pipeline engine. see https://github.com/microsoft/DeepSpeed/pull/1438
2. Move has_bool_tensors to kwargs to make usable with deepspeed.initialize and rename has to send. see https://github.com/microsoft/DeepSpeed/pull/1399
3. Add assertion to DS engine. see https://github.com/microsoft/DeepSpeed/issues/1034
4. Add @property to make module.mpu usable.
   • when we use PipelineEngine, we use syntax like engine.mpu. but when we use PipelineModule we must use module.mpu(). this can be confusing front end users.
   • So, I added @property to make module.mpu usable. We can use same syntax like something.mpu.
   • I also added __call__() method to PipelineParallelGrid to be compatible with exsting code

cc. @tjruwase

[rocm-mici]

Can one of the admins verify this patch?

[loadams]

Hi @hyunwoongko - apologies for taking so long to reply to this. Is this still a branch you'd like to see merged? If so, could you resolve merge conflicts? If not, we're closing and cleaning up old branches in the repo.