Stopping the Eiger whilst it's disarming causes issues

[DominicOram]

When a bluesky plan errors the RE will call stop on all the associated ophyd devices. In the Eiger stop/unstage are a very similar operation and touch basically the same PVs. We have an issue where we:

1. Start unstaging the Eiger
2. Have a failure in the plan (the failure in this case is no diffraction found so can be quite common)
3. This tries and stops the Eiger but the disarm is in progress causing a new exception

Acceptance Criteria

• When stop is called on the eiger, if a disarm is already in progress it just waits for the disarm