AutoYaST: write /etc/hosts even if keep_install_network=true (bnc#796580)

The regression was introduced in SP2 in yast2-network-2.17.166
(2012-01-13) in a fix for bnc#712864.
https://github.com/yast/yast-network/commit/4f67f62d9f16f774fac6870d932a53d1d29d10dc
There, a Lan::Read(`cache) call is added with the intent to merge in the
config provided by linuxrc; it also calls Host::Read, which should
always cache, but wrongly discards the Host::Import'ed data. So a later
Host::Write call thinks there is nothing new to write.
(y2log: "Host.ycp:153 Hosts not modified")

This is an incomplete fix for early testing. It should work
but leaves the code messy: `modified`, `initialized` and
`hosts_init` should all be merged.
(cherry picked from commit 2ddd18503743be8cf3155fbb840406d9c35d66d0)
AutoYaST: another write_hostname regression (bnc#796580)

If keep_install_network=true and dns/write_hostname is unspecified,
use the product default (which is false on SLES), thus not writing
127.0.0.2 to /etc/hosts.

(fixing a regression introduced in 2.17.166)
(cherry picked from commit 6d823622941df82c29ee321232bcb485f4ebc93c)
version + changes

note that the version number where the regression occured matches
the master branch (unlike in the cherry-picked parent commit)
Merge pull request #52 from mvidner/master

master: AutoYaST: fix interaction of keep_install_network, dns/write_hostname, hosts (bnc#796580)