[nailgun] Fix net check receiver.

It now handle 'networks' property of answer correctly.
[nailgun] Typo and after review fix.
[nailgun] New unit tests for net_verify rpc.
[net_probe] Fix for VID dups in forgotten place.
[nailgun] Fixes after review.

Fix error message when less than 2 nodes received.
Fix order of conditions to clearify error scenarios.
Error message contains interface.mac instead of node.mac.
[net_probe] Fix non-ascii symbols handling.
[fix] custom error message
[fix] error checking order
[rollback] error checking order and fix test
Merge pull request #1141 from Mirantis/docs

[docs] Added network issues section
Hacky fix for PRD-901
Disable some UI tests
Move hack to another place to make the tests pass
[docs] Added network timeout section
[docs] Updated networking diagram
[docs] Updated physical sample diagram
Some improvements about dnsmasq in documentation
Fix for test_network_config
Added tftp probe script
Merge pull request #1144 from Mirantis/docs

Docs