turn pg provision error into a warning

turn pg provision error into a warning

We haven't had any real cases of the PG "cant drop tables"
condition since this error was first introduced; instead we
seem to get it for a non-critical query during pool reconnect
tests, and I have not been able to isolate what is causing it.
Therefore turn the error into a new class of warning that can
emit within the test suite without failing the test, so that
if we do get a real PG drop timeout, the warning will be there
to show us what the query was in which it was stuck.

Change-Id: I1a9b3c4f7a25b7b9c1af722a721fc44ad5575b0f