packaging: setup: added upgrade from legacy plugins

Added plugins for detecting if we are upgrading from a
system installed using legacy setup.

- Set the environment variable CoreEnv.UPGRADE_FROM_LEGACY.
- Set FQDN from legacy sysconfig file if it exists (3.2.z).
- Set FQDN from existing config (legacy 3.3.z)
- Enable root redirection if upgrading from legacy 3.2.z.
- Force migration to Apache proxy when upgrading from legacy 3.2.z.
- Remove legacy sysconfig file if it exists (3.2.z).
- Set firewall manager (both legacy 3.2.z and 3.3.z).
- Set iso domain variables (both legacy 3.2.z and 3.3.z).
- Set AIO and data domain variables (both legacy 3.2.z and 3.3.z).
- Remove legacy ovirt-engine.conf (3.2.z).
- Add iso domain files to uninstall list (both legacy 3.2.z and 3.3.z).

Bug-Url: https://bugzilla.redhat.com/971327
Change-Id: I4ee25f561218d83c5a4bd821c2d89587df5bc47a
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>