Use variables in "components" property in app config JSON file

[Nathaniel Braun]

Hi,

In order to determine the principal name to use in my Kerberized AM, I need the 
hostname of the machine the AM executes on.

Here is the part of the appConfig.json I'm interested in:

  "components": {
    "slider-appmaster": {
      "jvm.heapsize": "256M",
      "slider.hdfs.keytab.dir": ".slider/keytabs",
      "slider.am.login.keytab.name": "httpfs.keytab",
      "slider.keytab.principal.name" : "${THIS_HOST}@{KERBEROS_REALM} "
    }

Basically, I need THIS_HOST and KERBEROS_REALM to be replaced with their actual 
values, coming from the AM's machine.

This does not work right now, those values are not interpreted.

Thanks for your help.

Regards,
Nathaniel