allow for not setting vpc_id

[phahulin]

It is possible to launch EC2 instance without vpc_id parameter, and playbook will use default one.
However, at the present moment vpc_id should be set in group_vars/all.yml anyway.

Is it possible to make it optional?

[ArseniiPetrovich]

Sure it is. We can simply default this to none and default parameter will be used. Just checked it.

[phahulin]

Ok, then this can be closed

[ArseniiPetrovich]

@phahulin Reopening this. vpc_id is falling to default parameters if not specified, but subnet_id
still needs to be explicitly set. This is not a bug itself, but we can definitely improve the playbooks and allow not to specify the subnet_id