These values have priority over ones defined in ironic.conf. Also modify
validation code to only used network UUID cached on task.network if:
1. the requested XXX_network is UUID, not name
2. the requested XXX_network is the same as the cached one.
Co-Authored-By: Dmitry Tantsur <dtantsur@redhat.com>
Closes-Bug: #1614876
Change-Id: I4caec34d85304fe887bcc28b7528cceceb3acfe8