[TASK] Speed up functional tests

Optimize functional test bootstrap to improve performance:

* Database schema for single tests of a test case are always
  identical by design. So a database can be re-used between
  single tests to save the table creation overhead. Database
  tables are truncated instead which is quicker.
* Load less extensions by default, so less tables are created.
* Enable class loader caches.

Typically, tests instances with mysql on a ramdisk, tests are ~25%
quicker, for native mysql on hdd the performance impact is ~50%.

Change-Id: Ife1ea755c5336f7d4362b2affe7bba9e94862e92
Resolves: #58433
Releases: 6.2