PCASpy: utf-8 error in log files

As a user I don't want my PCASpy server to be creating large log files with unhelpful errors. These were seen in the LSI Correlator IOC on both Zoom and Demo:

```
[2020-02-07 17:20:56] UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe8 in position 64: invalid continuation byte

[2020-02-07 17:21:32] UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 64: invalid start byte
```

These errors appear to be benign, but might contribute to large log files.

These might be related to this issue from pcaspy: https://github.com/paulscherrerinstitute/pcaspy/issues/59

This issue suggests that a client could be asking for a PV which is too long.
The LSI correlator is also our first pcaspy IOC to be running in python 3.

## Acceptance criteria:
- [ ] Cause of the errors is found
- [ ] These errors are no longer raised in LSI Correlator logs
- [ ] If applicable, fix is also prepared for other pcaspy drivers (remote IOC server, reflectometry)