MB-11344: Convert a temp item during an insert

- If a temp item is already found to exist during
warmup, then convert the temp item into a regular
item.

Change-Id: I12bc1ead075cb19f9ef397397f84abe6086f50e4
Reviewed-on: http://review.couchbase.org/38531
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>