tty: Clear tty before login: prompt by default, add 'noclear' option

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/tty.h

@@ -34,6 +34,7 @@ typedef struct {
 	char  *name;
 	char  *baud;
 	char  *term;
+	int    noclear;
 	int    runlevels;
 
 	int    pid;