Always log exceptions in rollbackMasterChangesAndLog()

Always log exceptions in rollbackMasterChangesAndLog()

MWExceptionHandler::rollbackMasterChangesAndLog() only logged exceptions
if there were already master changes. This is extremely problematic when
debugging, especially in situations like DeferredUpdates where they were
silently being swallowed.

This makes it log exceptions in all paths, erring on the side of logging
the same exception twice (theoretically it's possible I suppose) instead
of not at all.

Also make the method able to handle DBError exceptions, which most of
the callers seemed to be assuming. ApiMain was handling this explicitly.

Bug: T168347
Change-Id: I8739051f824a455ba669344184c3b11ac95cb561