build: target for go library dependencies

Didn't notice it because vendor/ was already populated on my dev
machine, but did notice it in Docker build.

Docker build now consumes devsetup like regular user, so this should
catch future problems.

Remove remaining curl|shit functionality from lazy.sh (no checkout logic
needed anymore).

refs #35

Makefile

@@ -1,4 +1,4 @@
-.PHONY: generate build test vet cover release docs docs-clean clean release-bins
+.PHONY: generate build test vet cover release docs docs-clean clean release-bins vendordeps
 .DEFAULT_GOAL := build
 
 ROOT := github.com/zrepl/zrepl
@@ -18,13 +18,17 @@ GO_LDFLAGS := "-X github.com/zrepl/zrepl/cmd.zreplVersion=$(ZREPL_VERSION)"
 
 GO_BUILD := go build -ldflags $(GO_LDFLAGS)
 
+vendordeps:
+	dep ensure -v -vendor-only
+
 generate: #not part of the build, must do that manually
 	@for pkg in $(_TESTPKGS); do\
 		go generate "$$pkg" || exit 1; \
 	done;
 
 build:
-		$(GO_BUILD) -o "$(ARTIFACTDIR)/zrepl"
+	@echo "INFO: In case of missing dependencies, run 'make vendordeps'"
+	$(GO_BUILD) -o "$(ARTIFACTDIR)/zrepl"
 
 test:
 	@for pkg in $(_TESTPKGS); do \
@@ -64,6 +68,7 @@ docs-clean:
 		BUILDDIR=../artifacts/docs
 
 release-bins: $(ARTIFACTDIR) vet test
+	@echo "INFO: In case of missing dependencies, run 'make vendordeps'"
 	GOOS=linux GOARCH=amd64   $(GO_BUILD) -o "$(ARTIFACTDIR)/zrepl-linux-amd64"
 	GOOS=freebsd GOARCH=amd64 $(GO_BUILD) -o "$(ARTIFACTDIR)/zrepl-freebsd-amd64"