fuel-nailgun-agent: ohai: Read L1 info w/ ethtool.

fuel-nailgun-agent: ohai: Read L1 info w/ ethtool.

fuel-nailgun-agent uses ohai and rethtool for reading eth info,
including ethernet card speed. However, current methods rely on the
drivers populating the advertised and/or supported link speed lists.

This is not true for all drivers, especially for some Fibers
that only report the speed via ethtool when the link is up.

This patch adds support for reading L1 info from ohai, which
supports parsing ethtool speed starting with version amos2 [1].

[1] https://linux.enea.com/mos-repos/ubuntu/8.0/pool/main/o/
    ohai/ohai_6.14.0-2~u14.04+mos1+mos8.0+amos2_all.deb

Change-Id: Ic8c252e411a680af32cc68574c572434147a7e78