Add KDbConnection::drv_getTableNames for low level list of table names, make tableNames() skip names with non-existing physical tables

Summary:

• KDbTestUtils: add convenience APIs for connecting and using db, support connection options, use it in parser test
• Add KDbConnection::drv_getTableNames for low level list of table names, make tableNames() skip names with non-existing physical tables
• This change is backward compatible since metadata without physical table is not usable anyway.

CCBUG:392112
FIXED-IN:3.2.0

+ Add autotest for handling missing physical tables

Test Plan: Run ctest

Reviewers: piggz

Tags: KDb

Differential Revision: https://phabricator.kde.org/D11547