Fixed cloning the Firewall settings

- Reading and adjusting the SuSEfirewall2 configuration has been moved from inst_finish to inst_proposal because AutoYast export can be already requested in inst_proposal
- bnc#887406

Not 100% related to this PR, but this reminded me to check the imports and SuSEFirewallProposal is imported in FirewallStage1FinishClient but never used.