[TASK] Unify installation tests

MySql receives a test to install the introduction package, PgSql gets
one for the blank page preset.
With this change, both install suites check both kind of setup the
instance.

Change-Id: Ic21091f5bc3a0aa14a49e9e9fa65a5f9db829cdb
Resolves: #83949
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/55770


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>