Add inline_comment_prefixes support to supervisorctl's config (for Py3)

I configured supervisorctl's configuration as follows:
```
[supervisorctl]
serverurl=unix:///tmp/supervisor.sock ; use a unix:// URL  for a unix socket
username=son                ; should be same as http_username if set
password=123                ; should be same as http_password if set
```
Next, I executed the command `supervisorctl` and the following error occurred:
```
[son@localhost ~]$ supervisorctl
unix:///tmp/supervisor.sock ; use a unix:/ URL  for a unix socket no such file
supervisor>
```