Adding exclude pattern file list param for rsync

As discussed in: vagrant-openstack-provider issue #166
rsync all files #166
Have a look at `initialize` and `finalize!` methods to see how array attributes are initialized. For instance, have a look at the `@networks` parameter. You should do the same for your new `@rsync_ignore_files`. Without those initializations there can be troubles in Vagrant during the Vagrantfile merge configuration step.