[BUFGIX] set password length to 8 in installtool

The installtool requires a password length of 8 letters,
but background of new password changes to yellow
after just 6 letters.

Resolves: #53159
Releases: 6.2
Change-Id: I6031e1a93af13f8db3fd1fb5a514da5746b7aa4e
Reviewed-on: https://review.typo3.org/25050
Reviewed-by: Steffen Müller
Tested-by: Steffen Müller
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind