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: I172b61d3fccc00e5951616646fa82e33b8322997
Implements: blueprint selectable-offloading-type

warpc/fuel-nailgun-agent