Add alternative method for specifying PLC IP address

[pcdshub]

Add alternative method for specifying PLC IP address

[klauer]

if they want to- the IOC should be able to run using this string, rather than an explicit IP, right?

Yes, asyn is backing ads-ioc and it does resolve hostnames without issue.
The above wording and example was very poor, but working with hostnames rather than IPs is definitely intended.

[ZLLentz]

I think the end goal should be allowing the user to specify plc_ip=my-plc-hostname in the Makefile if they want to- the IOC should be able to run using this string, rather than an explicit IP, right? Then your IOC build becomes resistant to adjustments to the IP configurations so long as your ams net id remains static. Options to pytmc stcmd seem like an appropriate path to fulfilling this.