[ENHANCEMENT] Default variables for ARG_REPLACEMENTS

[tobiastom]

Is your feature request related to a problem? Please describe.
Sometimes you need to configure a service with the IP or a hostname. With the new args/render feature inside Bastillefiles these could be provided by default.

Describe the solution you'd like
JAIL_NAME and JAIL_IP should be available as variables inside the Bastillefile and inside the render statement.

Describe alternatives you've considered
The solution to solve this right now is to always lookup and provide the values to the bastille template command:

bastille template lala foo/lala --arg JAIL_NAME=lala --arg JAIL_IP=192.168.1.1