Introduce a flag to allow use of kind in an idempotent fashion

[jbarrick-mesosphere]

What would you like to be added:

Introduce a --use-kind flag that is idempotent, meaning:

• if no cluster is running, start one (--start-kind)
• if a cluster is running, use it
• don't clean up the cluster at the end of the run (--skip-cluster-delete)

We can also deprecate --start-kind and instead of --skip-cluster-delete have --cluster-delete as an opt-in.

Why is this needed:

It is currently difficult to script usage of kuttl in a way that allows developers to easily iterate on the same kind cluster while developing. By introducing this flag they don't have to use different flags based on whether or not a kind cluster is already started, which can help simplify Makefiles (or, in many cases, destroying their kind cluster after every iteration).