Gather available offloading modes
Gather available offloading modes

Gather available offloading modes for physical interfaces
during the bootstrap stage. In this commit 'ethtool' util
output parsing approach has been used. Nailgun agent
collects modes and sent it to the nailgun API. These modes
will be parsed via nailgun and will be put into
offloading_modes JSON field of the interface db model.

Change-Id: Ic58abf4e4da30e6fd7320dd385c9ddee74057ee1
Implements: blueprint selectable-offloading-type

huntxu/fuel-web,nebril/fuel-web,stackforge/fuel-web,SmartInfrastructures/fuel-web-dev,prmtl/fuel-web,SmartInfrastructures/fuel-web-dev,prmtl/fuel-web,eayunstack/fuel-web,SmartInfrastructures/fuel-web-dev,huntxu/fuel-web,nebril/fuel-web,eayunstack/fuel-web,huntxu/fuel-web,prmtl/fuel-web,nebril/fuel-web,stackforge/fuel-web,stackforge/fuel-web,huntxu/fuel-web,prmtl/fuel-web,eayunstack/fuel-web,nebril/fuel-web,huntxu/fuel-web,SmartInfrastructures/fuel-web-dev,eayunstack/fuel-web,nebril/fuel-web,prmtl/fuel-web,eayunstack/fuel-web,SmartInfrastructures/fuel-web-dev