Wrong readback message on Ophyd devices with write_pv

If you create a device with a read_pv and write_pv that can't connect to the write_pv, the Ophyd traceback indicates that the failed connection occured on the read_pv, even if this PV exists.

Example:
The device returns 'Failed to connect to all signals: vpu.pitch_offset (SI-06SB:ID-VPU29:PitchOffset-Mon)' even though this PV exists and the error is occuring with the SI-06SB:ID-VPU29:PitchOffset-SP PV.

EpicsSignalWithMonSP("SI-06SB:ID-VPU29:PitchOffset", name="vpu_pitch_offset")

Start at the EpicsSignalWithMonSP entry point shown in the example and trace how its read_pv and write_pv connections are represented in the failure message. Reproduce the failed write_pv connection and verify that the traceback identifies SI-06SB:ID-VPU29:PitchOffset-SP rather than the existing read PV.

Written by the indexing model from the issue text.