Support autoscaling and test in CI

[sjpb]

Adds;

• Support for autoscaling via cloud-state nodes.
• CI for arcus and smslabs which test a mixed cloud/non-cloud cluster:
  • Test direct configuration of control, login + 2x compute
  • Test login + compute image build (in parallel with direct configuration, for speed)
  • Test reimage of login via openstack
  • Test reimage of compute via Slurm
  • Run test suite on 4x nodes (2x non-cloud + 2x cloud), testing autoscaling (uses predefined direct-mode ports for arcus, default new ports for smslabs)
• Support for using predefined ports for autoscaled nodes.
• A ResumeFail script which handles no node getting created and "not enough hosts available" errors.

NB 1: This is based off and supersedes #128.
NB 2: Requires the following merges, which will then need changes to dependencies:

• Autoscale and rebuild fixes ansible_collection_slurm_openstack_tools#42 (requirements.yml)
• Add ports to ResumeProgram ports and add ResumeFailProgram slurm-openstack-tools#16 (variable pytools_gitref)

Comments for release notes:

• Should now use openhpc_config_extra instead of overriding openhpc_config (there is a check that configless mode hasn't been disabled by such an override)