Update Makefile with several improvements

Especially but not limited to:
- make BINDDIR= ... - for when you don't want a bind mount at all
- make DOCSPORT=9000 docs - for when you want a not-8000 docs port
- when we can't determine a branch name, we don't try to "docker build -t docker: ." anymore - we just "docker build -t docker ." (thus allowing Docker to assume ":latest")

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

Makefile

@@ -1,14 +1,17 @@
 .PHONY: all binary build cross default docs docs-build docs-shell shell test test-integration test-integration-cli
 
-GIT_BRANCH := $(shell git rev-parse --abbrev-ref HEAD)
-DOCKER_IMAGE := docker:$(GIT_BRANCH)
-DOCKER_DOCS_IMAGE := docker-docs:$(GIT_BRANCH)
-
-# to allow `make BINDDIR=. shell`
+# to allow `make BINDDIR=. shell` or `make BINDDIR= test`
 BINDDIR := bundles
+# to allow `make DOCSPORT=9000 docs`
+DOCSPORT := 8000
 
-DOCKER_RUN_DOCKER := docker run --rm -i -t --privileged -e TESTFLAGS -v "$(CURDIR)/$(BINDDIR):/go/src/github.com/dotcloud/docker/$(BINDDIR)" "$(DOCKER_IMAGE)"
+GIT_BRANCH := $(shell git rev-parse --abbrev-ref HEAD 2>/dev/null)
+DOCKER_IMAGE := docker$(if $(GIT_BRANCH),:$(GIT_BRANCH))
+DOCKER_DOCS_IMAGE := docker-docs$(if $(GIT_BRANCH),:$(GIT_BRANCH))
+DOCKER_MOUNT := $(if $(BINDDIR),-v "$(CURDIR)/$(BINDDIR):/go/src/github.com/dotcloud/docker/$(BINDDIR)")
 
+DOCKER_RUN_DOCKER := docker run --rm -it --privileged -e TESTFLAGS $(DOCKER_MOUNT) "$(DOCKER_IMAGE)"
+DOCKER_RUN_DOCS := docker run --rm -it -p $(if $(DOCSPORT),$(DOCSPORT):)8000 "$(DOCKER_DOCS_IMAGE)"
 
 default: binary
 
@@ -22,10 +25,10 @@ cross: build
 	$(DOCKER_RUN_DOCKER) hack/make.sh binary cross
 
 docs: docs-build
-	docker run --rm -i -t -p 8000:8000 "$(DOCKER_DOCS_IMAGE)"
+	$(DOCKER_RUN_DOCS)
 
 docs-shell: docs-build
-	docker run --rm -i -t -p 8000:8000 "$(DOCKER_DOCS_IMAGE)" bash
+	$(DOCKER_RUN_DOCS) bash
 
 test: build
 	$(DOCKER_RUN_DOCKER) hack/make.sh binary test test-integration test-integration-cli