Move net_check into dhcp_checker package

Net_checker code should be moved to fuel-web repo
Write functional and ut's for net_check

Related to blueprint network-checker-add-unit-tests
Related to blueprint network-checker-move-in-fuel-web
Change-Id: Ie024d52caf5ab99a84eb080fdf6d021b488b033b
Merge "Move net_check into dhcp_checker package"