Vagrantfile: Add support for openSUSE Leap 42.3

Add support for provisioning kubespray on openSUSE Leap 42.3 virtual
machines.

Vagrantfile

@@ -18,6 +18,7 @@ SUPPORTED_OS = {
   "coreos-beta"   => {box: "coreos-beta",        bootstrap_os: "coreos", user: "core", box_url: COREOS_URL_TEMPLATE % ["beta"]},
   "ubuntu"        => {box: "bento/ubuntu-16.04", bootstrap_os: "ubuntu", user: "vagrant"},
   "centos"        => {box: "centos/7",           bootstrap_os: "centos", user: "vagrant"},
+  "opensuse"      => {box: "opensuse/openSUSE-42.3-x86_64", bootstrap_os: "opensuse", use: "vagrant"},
 }
 
 # Defaults for config options defined in CONFIG