cfg: When send_shutdown fails, clear shutdown_con

When (for example) CS_ERR_TRY_AGAIN is returned, shutdown_con was still
set resulting in following situation:
- It was not possible to call shutdown again
- Shutdown didn't proceed

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>
cfgtool: Retry shutdown on CS_ERR_TRY_AGAIN

It may be nice to deliver macro cs_repeat as default in some include
file.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>