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/go-retryablehttp/Makefile

@@ -0,0 +1,11 @@
+default: test
+
+test:
+	go vet ./...
+	go test -race ./...
+
+updatedeps:
+	go get -f -t -u ./...
+	go get -f -u ./...
+
+.PHONY: default test updatedeps