Make auto-revert-mode tests run faster

Make auto-revert-mode tests run faster

* test/lisp/autorevert-tests.el (auto-revert--timeout): Make into
defun and shorten timeout by a factor 10.
(auto-revert--wait-for-revert): Cut timeouts in half.
(with-auto-revert-test): New macro to set timeout to 0.1.
(auto-revert-tests--write-file): New defun.
(auto-revert-test00-auto-revert-mode)
(auto-revert-test01-auto-revert-several-files)
(auto-revert-test02-auto-revert-deleted-file)
(auto-revert-test03-auto-revert-tail-mode)
(auto-revert-test04-auto-revert-mode-dired)
(auto-revert-test05-global-notify)
(auto-revert-test06-write-file): Adapt test to run faster.  Remove
:expensive-test marks.

This was discussed in:
https://lists.gnu.org/r/emacs-devel/2020-10/msg01233.html