Beckhoff/tcioc: homing not working if limit is hit in direction of home

[rerpha]

As a developer I noticed on SANDALS that if a forward limit was hit you are then unable to forward home the axis, and if reverse is hit you are unable to reverse home. In the motor record for the beckhoff forward homes and reverse homes are functionally the same as the beckhoff handles homing itself. There must be something stopping this from occurring lower down - we should disable if possible.

Acceptance criteria

• I can forward home an axis even if the forward limit is engaged, and reverse home when the reverse limit is engaged
• a system test is added to prevent this from happening again

[rerpha]

from a brief look i can't see anything in the asyn motor record which would actually prevent homing if at a limit, but my guess is that it thinks it's already home as it's on the respective limit so doesn't bother doing anything...

[rerpha]

closed by #8037