Add tests for remote files in auto-revert-tests

* lisp/autorevert.el (auto-revert-debug): New defvar.
(auto-revert-notify-handler): Write traces.

* lisp/filenotify.el (file-notify-debug): New defvar.
(file-notify-handle-event, file-notify-callback): Write traces.

* lisp/net/tramp-sh.el (tramp-sh-handle-vc-registered):
Handle nil `vc-handled-backends'.

* test/lisp/autorevert-tests.el
(auto-revert-test-remote-temporary-file-directory): New defconst.
Handle also $REMOTE_FILE_NOTIFY_LIBRARY.
(auto-revert--test-enabled-remote-checked): New defvar.
(auto-revert--test-enabled-remote): New defun.
(auto-revert--wait-for-revert): Rewrite without timeout.
(auto-revert--deftest-remote): New defmacro.
(auto-revert-test01-auto-revert-several-files):
(auto-revert-test02-auto-revert-deleted-file): Adapt for remote files.
(auto-revert-test02-auto-revert-deleted-file):
Use `auto-revert-debug' for debug messages.
(auto-revert-test00-auto-revert-mode-remote)
(auto-revert-test01-auto-revert-several-files-mode-remote)
(auto-revert-test02-auto-revert-deleted-file-mode-remote)
(auto-revert-test03-auto-revert-tail-mode-mode-remote)
(auto-revert-test04-auto-revert-mode-dired-mode-remote): New tests.

* test/lisp/filenotify-tests.el (file-notify--test-event-handler):
Use `file-notify-debug' for debug messages.
2 jobs for master in 54 minutes and 10 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1629
test-all

00:54:10

passed #1630
test-filenotify-gio

00:39:01

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:315: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:290: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
make: *** [check-expensive] Error 2
Makefile:963: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1