Assign ZWE_haInstance_id before configmgr template resolution

[1000TurquoisePogs]

ZWE_haInstance_id is eithe rthe value of user input in the STC JCL, or the hostname.
The hostname lookup occurs in zwe (late) and the env var assignment happens then too.
This means template resolution, such as in the launcher itself, occurs before and this would fail:

zowe:
  cookieIdentifier: ${{ std.getenv('ZWE_haInstance_id') }}

if we can assign this value earlier, it'd be great to depend upon it as a reasonable default for some things.
Getting the hostname could be done by symbols on zos zowe/zowe-common-c#363 or a BPX command, but if the launcher is to be cross-platform in the future, not sure what's a better way. /etc/hostname is commonly used on unix.

[1000TurquoisePogs]

I can work on this, but it's not a priority right now so if someone else wants to give it a shot they can.

[1000TurquoisePogs]

I guess this function could be used from zowe-common-c
bpx doc