runfvp: reset the process group on startup

So that it is easy to kill runfvp and everything it starts (such as
telnet or the FVP itself), reset the process group on startup.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

scripts/runfvp

@@ -217,6 +217,9 @@ def runfvp(cli_args):
 
 if __name__ == "__main__":
     try:
+        # Set the process group so that it's possible to kill runfvp and
+        # everything it spawns easily.
+        os.setpgid(0, 0)
         runfvp(sys.argv[1:])
     except KeyboardInterrupt:
         pass