Refactor dhcp code, flake8 and pep8 fixes
Greatly improved code in dhcp checker. Fixed bug with dhcp behaviour on network down
For example of usage look at tests.py:TestDhcpWithNetworkDown
Add some description to tests. Remove print
Fixes accidently added debug code
Supress scapy logging on levels lower that ERROR
remove unnecessery headers
Merge pull request #1602 from Mirantis/fix/dhcp_bugs_and_refactoring

Fix/dhcp bugs and refactoring