Handle driver-specific mount creation and initialisation.

[wtgee]

In general the create_mount_from_config will need to handle specific cases that are different for each driver/model.

Original comment regarding mount:

                # TODO(jamessynge): We should move the driver specific validation into the driver
                # module (e.g. module.create_mount_from_config). This means we have to adjust the
                # definition of this method to return a validated but not fully initialized mount
                # driver.

Originally posted by @wtgee in https://github.com/panoptes/POCS/pull/852