Vagrantfile: Use rsync to copy working directory to VM

Depending on the VM configuration, vagrant may either use 'rsync' or
vboxfs for populating the working directory to the VM. However, vboxfs
means that any files created by the VM will also be present on the host.
As such, lets be explicit and always use 'rsync' to copy the directory
to the VM so we can keep the host copy clean. Moreover, the default
rsync options include '--copy-links' and this breaks rsync if there are
missing symlinks in the working directory like the following one:

Error: symlink has no referent:
"/home/user/kubespray/contrib/network-storage/glusterfs/group_vars"

As such, we override the default options to drop --copy-links.