First time mode for controller

- Upon first time invocation ``minio controller`` would create access keys and secret id
- Upon request passing 'keys' arg ``minio controller`` would provide the keys
- Add colorized notification

vendor/github.com/mattn/go-isatty/doc.go

@@ -0,0 +1,2 @@
+// Package isatty implements interface to isatty
+package isatty