Squish Tests: check_limit_violations motor function

As a developer I would like to verify the following behaviour using Squish:

- Set up a motor IOC (e.g. Galil).
- Create a block of the position PV.
- Run `check_limit_violations()` and verify that the function returns an empty array.
- Set the position to be under or over the Low or High limit.
- Run `check_limit_violations()` again and verify that the function returns an array with a single element being the block name.