netinfo: do not report broken networks

Function _getNetInfo() called from netinfo.py:get() raises IOError in
case when we try to get information about broken network (network with
non-existing interface).

This problem happens with ovirt-3.4, Fedora 20, python-ethtool 0.11

Problem is in _getNetInfo(), where we catch only errno.ENOENT.
- This is OK in ovirt-3.5 and master branch.
- In older branches (where we USE ETHTOOL in getIpInfo()), if defined
device is not found by getIpInfo(), errno.ENODEV is raised.
-> Due to this difference in error codes, parent function get() does not
get KeyError from getIpInfo() exception and therefore it does report
broken device.

Now _getNetInfo() catch errno.ENODEV too.

Change-Id: I1fa9173cb65d5140951c38d0cf1e49eb93222903
Signed-off-by: Petr Horáček <phoracek@redhat.com>
Label: ovirt-3.4-only
Bug-Url: https://bugzilla.redhat.com/1146960
Reviewed-on: http://gerrit.ovirt.org/33320
Reviewed-by: Dan Kenigsberg <danken@redhat.com>