Use gobin to fix version numbers of tools (#598)

I ran into a bunch of problems running goreleasers, and
some differences with goimports. This locks the versions
to versions that appear to work.

The goimports version is newer than the latest version run
on the repo, but it matches the version of Go used on the rest of
the project.

Makefile

@@ -6,6 +6,15 @@ github_repo := virtual-kubelet/virtual-kubelet
 binary := virtual-kubelet
 
 include Makefile.e2e
+# Currently this looks for a globally installed gobin. When we move to modules,
+# should consider installing it locally
+# Also, we will want to lock our tool versions using go mod:
+# https://github.com/golang/go/wiki/Modules#how-can-i-track-tool-dependencies-for-a-module
+gobin_tool ?= $(shell which gobin || echo $(GOPATH)/gobin)
+goimports := golang.org/x/tools/cmd/goimports@release-branch.go1.10
+gocovmerge := github.com/wadey/gocovmerge@b5bfa59ec0adc420475f97f89b58045c721d761c
+goreleaser := github.com/goreleaser/goreleaser@v0.82.2
+gox := github.com/mitchellh/gox@v1.0.1
 
 # comment this line out for quieter things
 # V := 1 # When V is set, print commands and build progress.
@@ -35,8 +44,8 @@ tags:
 	$Q @git tag
 
 .PHONY: release
-release: build $(GOPATH)/bin/goreleaser
-	goreleaser
+release: build goreleaser
+	$(gobin_tool) -run $(goreleaser)
 
 ##### =====> Utility targets <===== #####
 
@@ -84,7 +93,7 @@ list:
 	@echo "List..."
 	@echo $(allpackages)
 
-cover: $(GOPATH)/bin/gocovmerge
+cover: gocovmerge
 	@echo "Coverage Report..."
 	@echo "NOTE: make cover does not exit 1 on failure, don't use it to check for tests success!"
 	$Q rm -f .GOPATH/cover/*.out cover/all.merged
@@ -94,7 +103,7 @@ cover: $(GOPATH)/bin/gocovmerge
             -coverprofile=cover/unit-`echo $$MOD|tr "/" "_"`.out \
             $$MOD 2>&1 | grep -v "no packages being tested depend on"; \
     done
-	$Q gocovmerge cover/*.out > cover/all.merged
+	$Q $(gobin_tool) -run $(gocovmerge) cover/*.out > cover/all.merged
 ifndef CI
 	@echo "Coverage Report..."
 	$Q go tool cover -html .GOPATH/cover/all.merged
@@ -107,17 +116,18 @@ endif
 	@echo ""
 	$Q go tool cover -func .GOPATH/cover/all.merged
 
-format: $(GOPATH)/bin/goimports
+format: goimports
 	@echo "Formatting..."
 	$Q find . -iname \*.go | grep -v \
-        -e "^$$" $(addprefix -e ,$(IGNORED_PACKAGES)) | xargs goimports -w
+        -e "^$$" $(addprefix -e ,$(IGNORED_PACKAGES)) | xargs $(gobin_tool) -run $(goimports) -w
 
 
 
 ##### =====> Internals <===== #####
 
 .PHONY: setup
-setup: clean
+setup: goimports gocovmerge goreleaser gox clean
+	env
 	@echo "Setup..."
 	if ! grep "/bin" .gitignore > /dev/null 2>&1; then \
         echo "/bin" >> .gitignore; \
@@ -129,10 +139,6 @@ setup: clean
 	mkdir -p bin
 	mkdir -p test
 	go get -u github.com/golang/dep/cmd/dep
-	go get github.com/wadey/gocovmerge
-	go get golang.org/x/tools/cmd/goimports
-	go get github.com/mitchellh/gox
-	go get github.com/goreleaser/goreleaser
 
 VERSION          := $(shell git describe --tags --always --dirty="-dev")
 DATE             := $(shell date -u '+%Y-%m-%d-%H:%M UTC')
@@ -144,23 +150,27 @@ _allpackages = $(shell go list ./...)
 # memoize allpackages, so that it's executed only once and only if used
 allpackages = $(if $(__allpackages),,$(eval __allpackages := $$(_allpackages)))$(__allpackages)
 
+.PHONY: goimports
+goimports: $(gobin_tool)
+	gobin -d $(goimports)
+
+.PHONY: gocovmerge
+gocovmerge: $(gobin_tool)
+	gobin -d $(gocovmerge)
+
+.PHONY: goreleaser
+goreleaser: $(gobin_tool)
+	gobin -d $(goreleaser)
+
+.PHONY: gox
+gox: $(gobin_tool)
+	# We make gox globally available, for people to use by hand
+	gobin $(gox)
 
 Q := $(if $V,,@)
 
-
-$(GOPATH)/bin/gocovmerge:
-	@echo "Checking Coverage Tool Installation..."
-	@test -d $(GOPATH)/src/github.com/wadey/gocovmerge || \
-        { echo "Vendored gocovmerge not found, try running 'make setup'..."; exit 1; }
-	$Q go install github.com/wadey/gocovmerge
-$(GOPATH)/bin/goimports:
-	@echo "Checking Import Tool Installation..."
-	@test -d $(GOPATH)/src/golang.org/x/tools/cmd/goimports || \
-        { echo "Vendored goimports not found, try running 'make setup'..."; exit 1; }
-	$Q go install golang.org/x/tools/cmd/goimports
-
-$(GOPATH)/bin/goreleaser:
-	go get -u github.com/goreleaser/goreleaser
+$(gobin_tool):
+	GO111MODULE=off go get -u github.com/myitcv/gobin
 
 authors:
 	$Q git log --all --format='%aN <%cE>' | sort -u  | sed -n '/github/!p' > GITAUTHORS