Focus Move Bug

Bug reported by Hy whereby the final move to the optimum focus position failed (linear 1 pass).

Unclear exactly what happened from the log. Focus runs before and after went as expected. The most likely reasons:

1. Timing issue whereby focuser data was updated which being processed. Code change for this implemented.
2. Problem with messaging from focuser device, e.g. signalled IPS_OK before move completed. Added an extra log message to spot this scenario.