RFE: add possibility to overwrite RAM check

[ericzolf]

Since version 3.3.1 Tower raised the memory check to 4GB, which is quite high for a simple test VM.

I suspect that it should be sufficient to manipulate the inventory of setup.sh, by adding the variable required_ram set to the value of ansible_memtotal_mb in the section [all:vars].

Compare with:

./roles/preflight/defaults/main.yml:required_ram: 3750
./roles/preflight/tasks/main.yml:  when: ansible_memtotal_mb < required_ram|int