Use after-install && after-reset stages to initialize system

[anmazzotti]

Closes #806

The idea is that instead of generate several yip configs and pass them as ELEMENTAL_INSTALL_CLOUD_INIT list, we generate one single yip config to deterministically create the desired yip configs at desired locations. For example /oem/94_custom.yaml would always be /oem/elemental-network-config.yaml.

The after-install stage yip looks like the following (this sample only contains the registration config, the real one has all the other files):

name: Elemental Finalize System
stages:
    after-install:
        - files:
            - path: /run/elemental/oem/elemental-registration.yaml
              permissions: 384
              owner: 0
              group: 0
              content: |
                name: Include registration config into installed system
                stages:
                    initramfs:
                        - files:
                            - path: /oem/registration/config.yaml
                              permissions: 384
                              owner: 0
                              group: 0
                              content: |
                                elemental:
                                    registration:
                                        url: https://127.0.0.1.sslip.io/test/registration/endpoint
                                        ca-cert: a test ca
                                        emulate-tpm: true
                                        emulated-tpm-seed: 9876543210
                                        no-smbios: true
                                        auth: a test auth
                              encoding: ""
                              ownerstring: ""
                          if: '[ ! -f /oem/registration/config.yaml ]'
              encoding: ""
              ownerstring: ""
          directories:
            - path: /run/elemental/oem
              permissions: 448
              owner: 0
              group: 0
          name: Registration Config

I am not yet 100% sure that targeting /run/elemental/oem is the right thing to do during after-install or after-reset, but it does work.

[anmazzotti]

Still some issues with the after-reset hook.

The problem here is where to create the config, since:

1. /system/oem and /usr/local/cloud-config are read only in recovery.
2. /oem is formatted before the contents are evaluated

I think that adding /usr/local/cloud-config as ephemeral path in the recovery layout is a safe option to make this work.
/usr/local is by default a persistent path in the active system, but we don't mount any persistent path in recovery, so this solution would not collide with that (and with possible existing /usr/local/cloud-config/*.yaml files in the persistent partition) [Edit: Seems like mounting /usr/local/cloud-config in recovery breaks it, so this is not an option]

Another option would be to evaluate and cache all the /oem configs with after-reset* stages to be executed after formatting the OEM partition, but this feels a bit convoluted and hackish.

Probably the best solution would be to allow elemental-toolkit to consider dynamic config directories passed at runtime: elemental reset|install --evaluate-configs /tmp/my/custom/dir

[anmazzotti]

This PR now depends on rancher/elemental-toolkit#2163