docker: add environment variable PYTORCH_VERSION (pytorch#50154)

Summary:
The aim is being able to inspect a container image and determine immediately
which version of pytorch it contains.

Closes pytorch#48324

Signed-off-by: Felix Abecassis <fabecassis@nvidia.com>

seemethere PTAL.
As you requested in pytorch#48324 (comment), I'm submitting the patch. But I could only do limited testing as I'm not sure these Makefile/Dockerfile are used for pushing the Docker Hub images (since the Makefile tags the image with a `v` prefix for the version, as in: `pytorch:v1.7.1`, but Docker Hub images don't have this prefix).

Also on the master branch we currently have the following:
```
$ git describe --tags
v1.4.0a0-11171-g68a6e46379
```
So it's a little off, but it behaves as expected on the `release/1.7` branch.

Pull Request resolved: pytorch#50154

Reviewed By: walterddr

Differential Revision: D25828491

Pulled By: seemethere

fbshipit-source-id: 500ec96cb5f5da1321610002d5e3678f4b0b94b5

Dockerfile

@@ -59,6 +59,7 @@ RUN /opt/conda/bin/conda install -c "${INSTALL_CHANNEL}" -y python=${PYTHON_VERS
 RUN /opt/conda/bin/pip install torchelastic
 
 FROM ${BASE_IMAGE} as official
+ARG PYTORCH_VERSION
 LABEL com.nvidia.volumes.needed="nvidia_driver"
 RUN --mount=type=cache,id=apt-final,target=/var/cache/apt \
     apt-get update && apt-get install -y --no-install-recommends \
@@ -71,6 +72,7 @@ ENV PATH /opt/conda/bin:$PATH
 ENV NVIDIA_VISIBLE_DEVICES all
 ENV NVIDIA_DRIVER_CAPABILITIES compute,utility
 ENV LD_LIBRARY_PATH /usr/local/nvidia/lib:/usr/local/nvidia/lib64
+ENV PYTORCH_VERSION ${PYTORCH_VERSION}
 WORKDIR /workspace
 
 FROM official as dev

docker.Makefile

@@ -17,12 +17,14 @@ BASE_DEVEL                = nvidia/cuda:$(CUDA_VERSION)-cudnn$(CUDNN_VERSION)-de
 INSTALL_CHANNEL           = pytorch
 
 PYTHON_VERSION            = 3.7
+PYTORCH_VERSION           = $(shell git describe --tags)
 # Can be either official / dev
 BUILD_TYPE                = dev
 BUILD_PROGRESS            = auto
 BUILD_ARGS                = --build-arg BASE_IMAGE=$(BASE_IMAGE) \
 							--build-arg PYTHON_VERSION=$(PYTHON_VERSION) \
 							--build-arg CUDA_VERSION=$(CUDA_VERSION) \
+							--build-arg PYTORCH_VERSION=$(PYTORCH_VERSION) \
 							--build-arg INSTALL_CHANNEL=$(INSTALL_CHANNEL)
 EXTRA_DOCKER_BUILD_FLAGS ?=
 DOCKER_BUILD              = DOCKER_BUILDKIT=1 \
@@ -39,26 +41,26 @@ all: devel-image
 
 .PHONY: devel-image
 devel-image: BASE_IMAGE := $(BASE_DEVEL)
-devel-image: DOCKER_TAG := $(shell git describe --tags)-devel
+devel-image: DOCKER_TAG := $(PYTORCH_VERSION)-devel
 devel-image:
 	$(DOCKER_BUILD)
 
 .PHONY: devel-image
 devel-push: BASE_IMAGE := $(BASE_DEVEL)
-devel-push: DOCKER_TAG := $(shell git describe --tags)-devel
+devel-push: DOCKER_TAG := $(PYTORCH_VERSION)-devel
 devel-push:
 	$(DOCKER_PUSH)
 
 .PHONY: runtime-image
 runtime-image: BASE_IMAGE := $(BASE_RUNTIME)
-runtime-image: DOCKER_TAG := $(shell git describe --tags)-runtime
+runtime-image: DOCKER_TAG := $(PYTORCH_VERSION)-runtime
 runtime-image:
 	$(DOCKER_BUILD)
 	docker tag $(DOCKER_FULL_NAME):$(DOCKER_TAG) $(DOCKER_FULL_NAME):latest
 
 .PHONY: runtime-image
 runtime-push: BASE_IMAGE := $(BASE_RUNTIME)
-runtime-push: DOCKER_TAG := $(shell git describe --tags)-runtime
+runtime-push: DOCKER_TAG := $(PYTORCH_VERSION)-runtime
 runtime-push:
 	$(DOCKER_PUSH)