Add vagrant settings customization helpers
Helpers to allow overriding some Vagrant settings
(Customizations are based on plain-ruby file)
Switch to vagrant_config_helper for customizations
- Now it's using plain ruby to set customizable vagrant settings
- Includes support for overriding synced folders options
Merge pull request #279 from dbfit/vagrant-config-customization-yaml-to-plain-ruby

Vagrant config customization: support for synced folder options