opensuse.md

* Vagrantfile: Bump openSUSE to Leap 15.0

* roles: container-engine: Add 'containerd' package for openSUSE

The 'containerd' package contains the docker-containerd and
docker-containerd-shim binaries. We also need to ensure that the latest
version is installed since an older version may already be present (eg GCE
images)

* Remove docker log-opts for opensuse

* roles: bootstrap-os: Use lowercase 'o' for openSUSE

OpenSUSE is not a valid family name. The correct one is openSUSE

* roles: bootstrap-os: Update zypper cache before first installation

The zypper cache may be outdated so ensure that it's fully updated
before we try and install the bootstrap packages.