Add logging to network code

 - remove PrintLns from net-fence.main in favourite of log message
 - add logs for configureHost

Also remove commented test for AddDefaultGW because we don't have a good
way to test this without messing up the test machine's network.

[#83656106]
Split network management out of net_fence

Network configuration code shouldn't care about being a fence.

Also move low-level netlink wrapper code to devices subpackage, rename
"net-fence" package to "netfence" to fit better with golang package
naming and move devices fakes to their own fake package.

[#83656106]
Delete separate net_fence integration test

Too expensive for the benefit of two tests that are already covered (and
are better covered) by the main networking integration tests.

[#83656106]
Add logging and consistent errors when destroying network

[#83656106]