test: use --quick when starting emacs.

At least in emacs24, this removes the "site-lisp" directories from the
load path in addition to enforcing --no-site-lisp --no-init-file.

This works around a slightly mysterious bug on Debian that causes
test-lib.el not to load when there is cl-lib.el(c) in some site-lisp
directory.  It should be harmless in general since we really don't
want to load any files from addon packages to emacs.