Feat/longhorn replicas

[MiroslavRepka]

This PR fixes #564 by implementing the algorithm, run upon node deletion, which tries to create a new replica for the longhorn volume, if any replicas will be lost due to node deletion.

It also fixes a small bug, when deleting master nodes (case when the API endpoint was not defined).

An additional feature is the introduction of variadic functions for the kubectl package.

[MarioUhrik]

LGTM, if you've sufficiently tested that the new behavior is as you expect

[MiroslavRepka]

I tested it by deploying a cluster, creating a PV and

• deleting a single node, which holds a replica -> end state was correct
• deleting multiple nodes, each holding a replica -> end state was correct

I can run some additional tests if you would like @MarioUhrik

[MarioUhrik]

The tests you've done sound sufficient Miro, LGTM

[wULLSnpAXbWZGYDYyhWTKKspEQoaYxXyhoisqHf]

had a look, looks great, had some questions/suggestions.

[cloudziu]

LGMT!

[wULLSnpAXbWZGYDYyhWTKKspEQoaYxXyhoisqHf]

great stuff, LGTM, thanks @MiroslavRepka! 🚀