Allow some additional steps (including extracting kubeconfig and untainting) in phase run

[ratnopamc]

Problem description (if applicable)

For infrastructure providers such as capd, the airshipctl phase run involves doing some additional steps in between 2 phases. For instance, following operation is performed between phase controlplane-ephemeral and initinfra-networking-target .

airshipctl cluster get-kubeconfig > ~/.airship/kubeconfig-tmp
mv ~/.airship/kubeconfig-tmp "${KUBECONFIG}"

Additionally untainting of control plane nodes, setting of contexts (ephemeral and target clusters) are also performed outside of any phase run.
Currently there's no phase available to perform these steps. Once these phases are available, they can be included and executed as part of a phasePlan.

For a description of the workflow(for capd) can be found in https://github.com/airshipit/airshipctl/blob/master/docs/source/providers/cluster_api_docker.md#deploy-control-plane-and-workers . The scripts can be referenced in https://github.com/airshipit/airshipctl/tree/master/tools/deployment/provider_common directory.

Proposed change
Create phases and executors to execute additional steps that need to be performed for deployment of docker and cloud providers(capz, capg, capo).

Potential impacts
Potential security or performance related impacts.

[ratnopamc]

This issue can be closed. Fix for this issue has been merged.

[eak13]

Code has been merged. Closing.