Add a k3s data directory location specified by the cli

Need to add a cli flag for this. Also, should probably have config file loading support for the certificate commands.

Author: zhaileilei123

pkg/cli/cmds/certs.go

@@ -35,6 +35,11 @@ var (
 			Value:       "https://127.0.0.1:6443",
 			Destination: &ServerConfig.ServerURL,
 		},
+		cli.StringFlag{
+			Name:        "data-dir,d",
+			Usage:       "(data) Folder to hold state default /var/lib/rancher/" + version.Program + " or ${HOME}/.rancher/" + version.Program + " if not root",
+			Destination: &ServerConfig.DataDir,
+		},
 		cli.StringFlag{
 			Name:        "path",
 			Usage:       "Path to directory containing new CA certificates",