Fetch string to pass through writeTemporary() in DatabaseOracle.php

Pulled some code from insertOneRow() to fix the update() function
and prevent the error warnings in bugzilla 64970 from showing up.
Note that since insertOneRow() and update() contains a lot of
duplicate code, they may be candidates for merging, but that is
outside the scope of this request.

Bug: 64970
Change-Id: I9ff9077d68e77f05f878fc541f87e0a5ce86ecc2
(cherry picked from commit 176213b89849f849e2c8dad2f0a79747b18a8b9d)