Optionally use ssh settings only with vagrant ssh command

This allows bootstrapping the user on a base image, by using
default ssh settings during provisioning and user defined
ssh settings when doing `vagrant ssh`.

vagrant/lib/forklift/box_distributor.rb

@@ -60,8 +60,17 @@ def distribute!
  end
  end
 
- def fetch_from_box_or_settings(box, key)
- box.fetch(key) { @settings.fetch(key, nil) }
+ def fetch_setting(box, key, default = nil)
+ box.fetch(key) { @settings.fetch(key, default) }
+ end
+
+ def argv_include_any?(tokens)
+ tokens.any? { |token| ARGV.include?(token) }
+ end
+
+ def add_ssh_setting(box, machine, key)
+ return if (value = fetch_setting(box, "ssh_#{key}")).nil?
+ machine.ssh.send("#{key}=", value)
  end
 
  def define_vm(config, box = {})
@@ -71,9 +80,9 @@ def define_vm(config, box = {})
  machine.vm.box = box.fetch('box_name', nil)
  machine.vm.box_version = box.fetch('box_version', nil)
 
- %w[username forward_agent keys_only].each do |key|
- unless (value = fetch_from_box_or_settings(box, "ssh_#{key}")).nil?
- machine.ssh.send("#{key}=", value)
+ unless fetch_setting(box, 'use_ssh_settings_vagrant_ssh_only', false) && !argv_include_any?(%w[ssh ssh-config])
+ %w[username forward_agent keys_only].each do |key|
+ add_ssh_setting(box, machine, key)
  end
  end