Cleanup on failed `k8s bootstrap` an `k8s join-cluster` attempts

[neoaggelos]

Summary

Merge after #520

Changes

• Bootstrap control plane, bootstrap worker and join control plane hooks are refactored. We always defer a function that checks the result of the hook.
• In the case of preRemove, we simply log the error and proceed, otherwise the node is removed by microcluster peers but not the underlying dqlite database, breaking the cluster
• In the case of k8s bootstrap, remove all configs, stop control plane services, then use ResetClusterMember. This resets the microcluster state. Note that this runs automatically by k8sd, no manual action from the client is required.
• In the case of k8s join-cluster for worker nodes, similarly revert configs, then use ResetClusterMember
• In the case of k8s join-cluster for control plane nodes: When the postJoin hook runs, the node has already joined microcluster. Therefore, we need to revert configs, but also make sure to use DeleteClusterMember, such that the failed node is removed from the cluster before resetting.

Notes

• The wait for a node to be not Pending before removing has been moved to the k8s remove-node command, instead of delaying the completion of the k8s join-cluster command.