Add Support for Manta Object Storage as a Gateway (#5025)

Manta is an Object Storage by [Joyent](https://www.joyent.com/)

This PR adds initial support for Manta. It is intended as non-production 
ready so that feedback can be obtained.

vendor/github.com/joyent/triton-go/GNUmakefile

@@ -0,0 +1,47 @@
+TEST?=$$(go list ./... |grep -Ev 'vendor|examples|testutils')
+GOFMT_FILES?=$$(find . -name '*.go' |grep -v vendor)
+
+default: vet errcheck test
+
+tools:: ## Download and install all dev/code tools
+	@echo "==> Installing dev tools"
+	go get -u github.com/golang/dep/cmd/dep
+	go get -u github.com/golang/lint/golint
+	go get -u github.com/kisielk/errcheck
+	@echo "==> Installing test package dependencies"
+	go test -i $(TEST) || exit 1
+
+test:: ## Run unit tests
+	@echo "==> Running unit tests"
+	@echo $(TEST) | \
+		xargs -t go test -v $(TESTARGS) -timeout=30s -parallel=1 | grep -Ev 'TRITON_TEST|TestAcc'
+
+testacc:: ## Run acceptance tests
+	@echo "==> Running acceptance tests"
+	TRITON_TEST=1 go test $(TEST) -v $(TESTARGS) -run -timeout 120m
+
+vet:: ## Check for unwanted code constructs
+	@echo "go vet ."
+	@go vet $$(go list ./... | grep -v vendor/) ; if [ $$? -eq 1 ]; then \
+		echo ""; \
+		echo "Vet found suspicious constructs. Please check the reported constructs"; \
+		echo "and fix them if necessary before submitting the code for review."; \
+		exit 1; \
+	fi
+
+lint:: ## Lint and vet code by common Go standards
+	@bash $(CURDIR)/scripts/lint.sh
+
+fmt:: ## Format as canonical Go code
+	gofmt -w $(GOFMT_FILES)
+
+fmtcheck:: ## Check if code format is canonical Go
+	@bash $(CURDIR)/scripts/gofmtcheck.sh
+
+errcheck:: ## Check for unhandled errors
+	@bash $(CURDIR)/scripts/errcheck.sh
+
+.PHONY: help
+help:: ## Display this help message
+	@echo "GNU make(1) targets:"
+	@grep -E '^[a-zA-Z_.-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-15s\033[0m %s\n", $$1, $$2}'