Issue: #307 added module_defaults action groups

[sumanth-lingappa]

All netscaler.adc collection modules have a common set of args (nsip, nitro_user, nitro_pass1 etc). There are three ways these common args can be specified in the playbook

1. specify these for every playbook-ask -- will be cumbersome (takes unnecessary lines)
2. specify environment variables -- Refer to playbook_anatomy.md
3. provide module_defaults per playbook -- THIS IS THE NEW IMPLEMENTATION IN THIS PR