We've seen reports that extra data sometimes contains empty lists.
There is no point to discard everything in this case. This change
makes ironic-inspector log a warning for any item of incorrect length
by default. The old behavior can be returned via [extra_hardware]strict.
Also stops discarding the received data if parsing fails: maybe this
data is not for us?
Change-Id: I1af55fa4ec47b345479b9e5687ad480648e502ac