environment: make the reproducible environment available via shlib use

environment: make the reproducible environment available via shlib use

Make the reproducible enviornment (with a controlled HOME dir) available
simply by running shlib.sh.  In most cases this would already have been
set either via taskd.pl or jobd.pl or git-http-backend-verify or by the
git() function, but just to make sure, move the settings outside any
function so that any scripts that might be run by hand end up with the
same environment as those run automatically.

While we're moving things around, also make the $chroot/etc/girocco
directory have no write permissions (after creating the contained
.gitconfig with write permissions for $mirror_owner).  This prevents
any foreign vcs "helpers" from leaving turds behind.