Test https://github.com/canonical/cluster-api-k8s/pull/195

snap-k8s: do not use the snap install dangerous flag

When using the `snap install --dangerous <path_to_local_snap_binary>`,
the revision is set to `x1` instead of the real revision.

This behaviour breaks the rolling upgrade for the minor k8s versions,
as the rolling upgrade needs an actual revision number.

Fixes: https://github.com/canonical/cluster-api-k8s/issues/193