add support for custom global options in AD DC confgurations

[phlogistonjohn]

This revisits and reuses parts of the work done in #45
Fixes: #43

When replying to samba-in-kubernetes/samba-container#154 I realized that one of the workarounds I suggested could be implemented in sambacc without too many complications and without needing to change samba-tool. Also, all versions of samba used by samba-container images that provide AD DC images should be providing the smbconf python library now. This avoids us having to parse smb.conf-style-ini in python.

Briefly, when an AD DC configuration provides globals references the global options are passed directory to samba-tool commands and after samba-tool has generated an smb.conf, sambacc uses smbconf libraries to read the smb.conf, merge the settings from the sambacc globals and write out an updated smb.conf file.

An example YAML configuration file I manually tested with:

samba-container-config: v0
configs:
  demo:
    instance_features: [addc]
    domain_settings: sink
    instance_name: dc1
    globals: ["adglobals"]
domain_settings:
  sink:
    realm: DOMAIN2.SINK.TEST
    short_domain: DOMAIN2
    admin_password: Passw0rd
domain_groups:
  sink:
    - name: peeps
domain_users:
  sink:
    - name: bwayne
      password: "1115Rose."
      given_name: Bruce
      surname: Wayne
      member_of: ["peeps"]
globals:
  adglobals:
    options:
      "dns forwarder": "192.168.64.1"
      "ldap server require strong auth": "no"
      "ignore:me": "yes"

Results in an smb.conf like:

[global]
        dns forwarder = 192.168.64.1
        netbios name = dc1
        realm = DOMAIN2.SINK.TEST
        server role = active directory domain controller
        workgroup = DOMAIN2
        idmap_ldb:use rfc2307 = yes
        ignore:me = yes
        ldap server require strong auth = no

[sysvol]
        path = /var/lib/samba/sysvol
        read only = No

[netlogon]
        path = /var/lib/samba/sysvol/domain2.sink.test/scripts
        read only = No

Using dig in the container I was able to test that dns forwarder option did have an actual effect on the running samba server.

---

The PR starts off with a few random cleanups of stuff that I hit while working on these changes. If you'd rather see those as a separate PR, just ask.

This doesn't update any docs. I will update the documentation in a separate PR, perhaps after asking the issue reporters to test out the changes when they land in samba-container server & ad-server latest images on quay.

[synarete]

Overall, look fine. I would prefer modern pathlib.Path over traditional os APIs.

[synarete]

lgtm

[anoopcs9]

We already support custom options in non AD DC setup, right?

[phlogistonjohn]

We already support custom options in non AD DC setup, right?

If I understand the question right, then yes.

sambacc initially only knew how to provision the AD DC, which generates it's own smb.conf but still had a place in it's own config for specifying globals, they were just ignored. This PR aims to make it work - and it's one of the more requested things for users of samba-containers.