[FOLLOWUP][BUGFIX] Reestablish DB connection in long-running tasks

Reconnecting in isConnected() is not necessary as the next query() will
check the status and reconnect properly if required. Using ping() does
not work with mysqlnd - only if mysqli.reconnect=1 is set. Setting this
is bad practice since a ping() would only reconnect but not properly
reinitialize the charset etc.

Thus a check in Install Tool is added to make sure mysqli.reconnect is
set to "0".

Resolves: #69001
Resolves: #69289
Releases: master, 6.2
Change-Id: I3c2cac91e96fdee8bff113f848341856ec51829b
Reviewed-on: http://review.typo3.org/42893


Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>