Add documentation on DHCP for private networking
guests/{free,net}bsd: add `insert_public_key` capability

Copy the cap to missing *bsd variants.
Merge pull request #2931 from rmccue/patch-1

website/docs: Add documentation on DHCP for private networking
website/docs: use string instead of symbol
guests/linux: don't chown VB shared folders if readonly [GH-2442]
kernel/v2: default all configs properly, remove config/default.rb
website/docs: clarify plugin development with latest changes
website/docs: update plugin usage docs
website/docs: clarify Vagrantfile/config loading order
core: config raises NoMethodError on bad calls once finalized
Fix tests for new _finalize! changes
core: tests around the environment setup_version
core: use a Monitor in BoxCollection
core: upgrade to v1.5 box dir format if it can
core: error if newer home dir version is detected
core: BoxCollection#all returns versions
core: BoxCollection can find with version constraints
core: all box collection tests pass
core: Box has a version field
core: boxcollection test tests versions