Add support for SSE-S3 server side encryption with vault (#6192)

Add support for sse-s3 encryption with vault as KMS.

Also refactoring code to make use of headers and functions defined in
crypto package and clean up duplicated code.

vendor/github.com/hashicorp/hcl/Makefile

@@ -0,0 +1,18 @@
+TEST?=./...
+
+default: test
+
+fmt: generate
+	go fmt ./...
+
+test: generate
+	go get -t ./...
+	go test $(TEST) $(TESTARGS)
+
+generate:
+	go generate ./...
+
+updatedeps:
+	go get -u golang.org/x/tools/cmd/stringer
+
+.PHONY: default generate test updatedeps