Add possibility to add several interfaces on 1 L2

Modified describe_environment, create_interfaces,
set_network methods so that they use bonding
parameters of settings.py module. Added new
parameters to settings.py that allow bonding.

Closes-Bug: #1301834

Change-Id: Ifd8f99596ce79f08d99bc99743a97df9884a4724
Merge "Add possibility to add several interfaces on 1 L2"