makefile_base.mak: Export HOME in container invocation

This was causing weird bugs in docker-on-OS X which wasn't determining
home correctly.  (Not really a supported setup)

build/makefile_base.mak

@@ -51,7 +51,7 @@ export CC
 export CXX
 
 # Selected container mode shell
-DOCKER_SHELL_BASE = sudo docker run --rm --init -v $(HOME):$(HOME) -w $(CURDIR) \
+DOCKER_SHELL_BASE = sudo docker run --rm --init -v $(HOME):$(HOME) -w $(CURDIR) -e HOME=$(HOME) \
                                     -v /etc/passwd:/etc/passwd:ro -u $(shell id -u):$(shell id -g) -h $(shell hostname) \
                                     -v /tmp:/tmp $(SELECT_DOCKER_IMAGE) /dev/init -sg -- /bin/bash