kvm tools: Set active console before running /bin/sh

This patch sets active console to the serial console before running the
shell. Doing so fixes two issues:

* Fix job control.

* Set all env vars.

The user visible issues are less warnings (no more of this:
  sh: cannot set terminal process group (-1): Inappropriate ioctl for device
  sh: no job control in this shell)

A working 'top', and a working ctrl-c.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

guest/init.c

@@ -11,7 +11,7 @@
 static int run_process(char *filename)
 {
 	char *new_argv[] = { filename, NULL };
-	char *new_env[] = { NULL };
+	char *new_env[] = { "TERM=linux" };
 
 	return execve(filename, new_argv, new_env);
 }
@@ -30,6 +30,12 @@ int main(int argc, char *argv[])
 
 	do_mounts();
 
+        /* get session leader */
+        setsid();
+
+        /* set controlling terminal */
+        ioctl (0, TIOCSCTTY, 1);
+
 	puts("Starting '/bin/sh'...");
 
 	run_process("/bin/sh");