Do not update node info when network data is corrupted

Deployment process introduces a lot of disruptive changes
in system configuration which can lead to undesirable state in
nailgun db

As solution - update only timestamp when network data is incorrect

This fix will protect nailgun against wrong network data stored in db
that maybe generated during process of network configuration on slave

See latest comment on bug for such case description

Change-Id: I2d67f851cf0e99f04b50611787e4872193212540
Closes-Bug: #1304469
Merge "Do not update node info when network data is corrupted"