Improve substitution of the all: statement

Improve substitution of the all: statement

We now substitute the all: statement in 3 stages:

1. We check if we get a setting for it which states which machines
should substitute all: (The setting is not fully implemented yet but all
changes which need to be done in recipe.py are done)

2. We try to get all machines named in the recipe and try to substitute
all: with these list.

3. If all other methods faile dwe substitute all: with all amchines
named in the virtual environment.

Signed-off-by: Jonatan Schlag <jonatan.schlag@ipfire.org>