Rsync folders by Vagrant core code

Vagrant 1.5 introduced a common logic for folder synchronization for all plugins ([Rsync Synced Folders](http://www.vagrantup.com/blog/feature-preview-vagrant-1-5-rsync.html)).

RSync-related code is now moved into Vagrant core, and maintained by Mitchell directly.
In vSphere plugin we need to get new bugfixes, for example https://github.com/mitchellh/vagrant/pull/3804.

So duplicated and outdated Rsync-related code is removed, and inherited from Vagrant core.

Additionally I raise a requirement for minimal compatible Vagrant version to 1.5.