GitLab

**Description**
This commit fixes the URL of ROCm GPG file.

**Description**
Add gpcnet as git submodule and building logic.

**Major Revision**
- add gpcnet as a submodule
- add build logic in third_party/Makefile

__Description__

Resolve "too many open files" issue when runnning NCCL/RCCL on multiple nodes using Docker images, increase nofile number in limits.conf.

**Description**
Install openmpi-4.0.0 for ROCm images.

**Description**
Setup docker environment in docker container.

**Major Revision**
- Install docker client for cuda and rocm images.
- Mount /var/run/docker.sock from host

**Description**
Add dockerfile `rocm4.0-pytorch1.7.0.dockerfile` and `rocm4.2-pytorch1.7.0.dockerfile` for `rocm` platform.