[WIP] Try using plain vagrant-berkshelf instead of vagrant-toplevel-cookbooks

[tknerr]

This is a try of using vagrant-berkshelf only for resolving multiple disjoint (top level) cookbooks that make up a multi-vm infrastructure.

If this works this essentially makes the vagrant-toplevel-cookbooks plugin unnecessary.

According to the docs it should work by

• using the groups feature of berkshelf
• defining one group per VM
• running berks vendor --only <group> for each VM separately

However, I could not get it to work so far (using berkshelf 3.2.3 and vagrant-berkshelf 4.0.2). Problems are:

1. berks install --only does not work
2. even if it worked, it seems it would use only a sinlge Berksfile.lock. Not sure how that would work out in a multi-vm setup