ICSHWI-9715 No pvget if systemd service is not running

Check if the systemd service of the IOC is running and do not issue a pvget if not. It is done by checking if /run/ioc@sluggified_ioc_name exists. Can still lead to timeouts if the service is running but the IOC has problems or the PV is not available but at least we can reduce network traffic when the IOC is obviously not running

Dear @andersharrisson, could you please merge this? (No need to tag it just yet; still working on other improvements)

Thanks!