[BUILD] Generalize our options passed to docker-run

Running things under docker will have various options
in common, so lets capture this in a way to promote
reuse.

For instance, we always want to:
  * volume mount fabric.git to $GOPATH and set WORKDIR
  * use -i --rm
  * optionally use --user

Change-Id: Iddca0d25fd0f08b34c2b1e5fbd10dd49def3351f
Signed-off-by: Greg Haskins <gregory.haskins@gmail.com>

Makefile

@@ -48,14 +48,22 @@ endif
 PKGNAME = github.com/$(PROJECT_NAME)
 GO_LDFLAGS = -X $(PKGNAME)/metadata.Version=$(PROJECT_VERSION)
 CGO_FLAGS = CGO_CFLAGS=" " CGO_LDFLAGS="-lrocksdb -lstdc++ -lm -lz -lbz2 -lsnappy"
-UID = $(shell id -u)
 ARCH=$(shell uname -m)
+OS=$(shell uname)
 CHAINTOOL_RELEASE=v0.10.0
 BASEIMAGE_RELEASE=$(shell cat ./.baseimage-release)
 
 DOCKER_TAG=$(ARCH)-$(PROJECT_VERSION)
 BASE_DOCKER_TAG=$(ARCH)-$(BASEIMAGE_RELEASE)
 
+ifneq ($(OS),Darwin)
+DOCKER_FLAGS=--user=$(shell id -u)
+endif
+
+DRUN = docker run -i --rm $(DOCKER_FLAGS) \
+	-v $(abspath .):/opt/gopath/src/$(PKGNAME) \
+	-w /opt/gopath/src/$(PKGNAME)
+
 EXECUTABLES = go docker git curl
 K := $(foreach exec,$(EXECUTABLES),\
 	$(if $(shell which $(exec)),some string,$(error "No $(exec) in PATH: Check dependencies")))
@@ -117,11 +125,11 @@ linter: gotools
 %/bin/protoc-gen-go: Makefile
 	@echo "Building $@"
 	@mkdir -p $(@D)
-	@docker run -i \
-		--user=$(UID) \
+	@$(DRUN) \
 		-v $(abspath vendor/github.com/golang/protobuf):/opt/gopath/src/github.com/golang/protobuf \
 		-v $(abspath $(@D)):/opt/gopath/bin \
-		hyperledger/fabric-baseimage:$(BASE_DOCKER_TAG) go install github.com/golang/protobuf/protoc-gen-go
+		hyperledger/fabric-baseimage:$(BASE_DOCKER_TAG) \
+		go install github.com/golang/protobuf/protoc-gen-go
 
 build/bin/chaintool: Makefile
 	@echo "Installing chaintool"
@@ -139,11 +147,9 @@ build/docker/bin/%: $(PROJECT_FILES)
 	$(eval TARGET = ${patsubst build/docker/bin/%,%,${@}})
 	@echo "Building $@"
 	@mkdir -p build/docker/bin build/docker/pkg
-	@docker run -i \
-		--user=$(UID) \
+	@$(DRUN) \
 		-v $(abspath build/docker/bin):/opt/gopath/bin \
 		-v $(abspath build/docker/pkg):/opt/gopath/pkg \
-		-v $(abspath .):/opt/gopath/src/$(PKGNAME) \
 		hyperledger/fabric-baseimage:$(BASE_DOCKER_TAG) \
 		go install -ldflags "$(GO_LDFLAGS)" $(pkgmap.$(@F))
 	@touch $@