Remove multi-cluster SNO complications.

[dbutenhof]

Jetlag will always create a single cluster, whether single or multi-node. SNO inventory discovery will comment all "free" machines past the first, and deployment will always work on the single uncommented machine, removing the sno_node_count variable. You can manually move the comment and re-run the sno-deploy.yml playbook to deploy additional SNO clusters if there are remaining nodes.

This PR refactors the SNO-specific logic from the sno-generate-discovery-iso and sno-install-cluster roles into the generate-discovery-iso and install-cluster roles, without the multi-cluster looping.

The remaining sno roles will be handled in subsequent individual PRs.