support user specified rsync excludes.

This commit allows to specify subfolders that should be excluded from syncing via synced_folder options:
e.g.:
config.vm.synced_folder '.', '/vagrant', :rsync_excludes => ['chef/tmp', 'tmp']
use latest vagrant
Merge branch 'rsync_excludes' of github.com:databus23/vagrant-aws into databus23-rsync_excludes

Conflicts:
	lib/vagrant-aws/action/sync_folders.rb