Make sure zseries.prepare do not move the axis

Closes #157 (closed)

The code use inside Daiquiri to get the estimation time is moving the z motor.

It is due to the fact prepare move the z axis at the first step, like if it the first fullfield.

This PR is a work around to make it work. Filtering the very first call.

Plus a test the same way Daiquiri get the estimation time.