.deb/.rpm: various fixes related to non-root

* Explicitly chown /var/lib/osmocom to osmocom:osmocom, instead of
  relying on systemd to do it when the service starts up. This does not
  work with the systemd versions in debian 10 and almalinux 8.
* deb: Use "useradd" instead of the interactive "adduser" perl script
  from Debian. This makes it consistent with how we do it in rpm, and
  avoids the dependency on "adduser".
* deb: Consistently use tabs through the file, instead of mixing tabs
  and spaces.
* deb: Remove support for the "dpkg-statoverride --list" logic. This
  seems to be a rather obscure feature to override permissions for
  certain files or directories, for which it does not seem to be a good
  idea to make the postinst script less maintainable. Something similar
  can be achieved by using your own Osmocom config file in a different
  path with different permissions.

Related: OS#4107
Change-Id: I6dd0205fb65d4ad5a79821c111865e67fb293a73

debian/control

@@ -30,7 +30,7 @@ Homepage: https://projects.osmocom.org/projects/osmo-hnodeb
 Package: osmo-hnodeb
 Architecture: any
 Multi-Arch: foreign
-Depends: ${misc:Depends}, ${shlibs:Depends}, adduser
+Depends: ${misc:Depends}, ${shlibs:Depends}
 Recommends: osmo-mgw
 Description: OsmoHNodeB: Osmocom's Home NodeB for 3G mobile networks