use g_path_get_basename instead of basename

use g_path_get_basename instead of basename

basename(3) and dirname(3) modify their argument and may return
pointers to statically allocated memory which may be overwritten by
subsequent calls.
g_path_get_basename and g_path_get_dirname have no such issues, and
therefore more preferable.

Signed-off-by: Julia Suvorova <jusual@mail.ru>
Message-Id: <1519888086-4207-1-git-send-email-jusual@mail.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>