ssl: Set a global boolean to enable SSL across Minio (#3558)

We have been using `isSSL()` everywhere we can set
a global value once and re-use it again.

cmd/update-main.go

@@ -265,12 +265,8 @@ func getReleaseUpdate(updateURL string, duration time.Duration) (updateMsg updat
 
 // main entry point for update command.
 func mainUpdate(ctx *cli.Context) {
-
-	// Set global variables after parsing passed arguments
-	setGlobalsFromContext(ctx)
-
 	// Initialization routine, such as config loading, enable logging, ..
-	minioInit()
+	minioInit(ctx)
 
 	if globalQuiet {
 		return