Allow QUIET=0 as temporary fix in installation scripts

[vmcj]

I encountered this when changing our update_*.sh scripts. We use QUIET=1 there, I replaced that with QUIET=0 which would enter 0 in a couple of places where we don't really need that. The same would happen with QUIET=2 which would be a strange but valid boolean.

Those fixes should make it hopefully easier to read and remove this specific issue. I couldn't find a nice way to do an or to remove the duplication so we end up with some (ugly) replication of the flags.

[eldering]

I'm fine with adding QUIET_FLAG{,_CAPITAL}, but I think right now the difference (if any?) between specifying QUIET=0 or nothing is unclear.
I'd rather not have that difference at all, or if really necessary clearly document why/where that's needed.

[vmcj]

I'm fine with adding QUIET_FLAG{,_CAPITAL}, but I think right now the difference (if any?) between specifying QUIET=0 or nothing is unclear. I'd rather not have that difference at all, or if really necessary clearly document why/where that's needed.

I was debugging the demoweb instance, where we have QUIET=1 in the scripts. As not all files are versioncontrolled I rather change the QUIET=1 to QUIET=0 as that way I can easily check where I should fix the option again after I was done on the demoweb fixing.

So I propose that we have:

Verbose:
QUIET=
QUIET=0

Quiet:
QUIET=1...

Which I think all reflect normal boolean rules and feel intuitive to me.