Database: Avoid internal use of ignoreErrors()

Database: Avoid internal use of ignoreErrors()

* Use $tempIgnore in DatabaseBase::tableExists() instead of ignoreErrors().
* DatabasePostgres::reportQueryError(), since 419221e4a71b, calls
  ignoreErrors() before and after rollback(). This is probably not effective
  as a recursion guard (reportQueryError() would be called regardless), and
  for suppressing any log entry or exception, it is redundant (doRollback()
  already sets $tempIgnore when calling query()).
* ignoreErrors(), now unused, can be removed in a separate change set.

Change-Id: Iee768abf996ece213146ab8f64a15a2b407a2e5e