installer: tell anaconda to leave firewall alone
installer: tell anaconda to leave firewall alone

Take advantage of `firewall --use-system-defaults` [1]
so that we can embed firewalld [2] but leave it disabled.
This was done in fedora lorax templates as well [3].

[1] https://github.com/rhinstaller/anaconda/pull/1271
[2] https://pagure.io/fedora-atomic/pull-request/103
[3] https://pagure.io/fedora-lorax-templates/pull-request/25

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