qrexec: make the log writable by qubes group

Otherwise if VM was started as root, it will never start as normal user
again.

qrexec/qrexec-daemon.c

@@ -273,7 +273,7 @@ void init(int xid)
     umask(0007);        // make the log readable by the "qubes" group
     logfd =
         open(qrexec_error_log_name, O_WRONLY | O_CREAT | O_TRUNC,
-         0640);
+         0660);
 
     if (logfd < 0) {
         perror("open");