netinfo: Report current system values for bonding options

Instead of reading bonding options from ifcfg files,
use /sys/class/net/BONDNAME/bonding to fetch "live" values.
Return only those that differ from defaults, introduced in b3f6e0.

The options are presented in two ways: as a "legacy" string of
opt=value pairs, separated by spaces, known from ifcfg files,
and as a dictionary with option names as keys and with arrays
of strings as values. The arrays can contain a single string
if an option is numerical or two strings if an option is symbolic
(name first, code second).

A bond info dictionary can look like this (abriged):
'bond4': {
    'cfg': {'BONDING_OPTS': 'miimon=150 mode=3'},
    'options': {'miimon': ['150'], 'mode': ['broadcast', '3']}
}

Functional network tests now check that bonding options were
applied.

Change-Id: Ief6d366b1b761627c7203cf236b75ef538af3e26
Bug-Url: https://bugzilla.redhat.com/987813
Signed-off-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24456
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>