Fix early-exit in cleanupOneNode

node.state_time is a time.time() value, which is never < 900, so the
early exit just wasn't happening.

Change-Id: I18f4745ec8bbcfca1807fb303ff84521858492e9
Avoid redundant updates of node.state=DELETE.

These break the timestamp for the state duration as well as making
concurrent deletes (CLI + nodepoold) worse by writing when we don't
need to, causing a DB row lock.

Change-Id: I45ed566764bcff3e548ea0dd2fb1ecfd4a284069
Log the time a node has been in state DELETE.

Previously we logged the time spent in deleteNode which can be
dramatically different - for instance when the 10 minute timeout
expires, we don't delete the node, and when periodic cleanup does
delete the node it will be gone already so we may only spend seconds
doing the deletion. The total elapsed time is actually much more
interesting.

Change-Id: If5a4561262663fcf265c3060a2034901cd8a8c3c