apache: Don't restart daemon when changing certificates

Fixes: #2271

When domain name is updated, it usually results in a error page as the HTTP
connection is broken in the middle of a page load. This is due to apache
restarting in the middle of domain change operation by letsencrypt component.
This also leads to several functional tests failing. To fix this, ensure that
letsencrypt does a reload on the apache2 daemon instead of restarting it.

'reload' operation on apache2 triggers the command 'apachectl graceful'. It
ensures that currently running continue to serve the open HTTP connection until
the page load has been completed. After that those connections stop. Meanwhile,
the server reloads configuration (and apparently the related TLS certificates too).

Tests:

- Unit tests pass.
- When self-signed certificate is updated with 'make-ssl-cert
  generate-default-snakeoil --force-overwrite' and 'systemctl
  try-reload-or-restart apache2' is called, the new certificate is loaded by
  apache2. Browser shows the untrusted certificate warning again. The
  certificate information in the connection details has been updated.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

plinth/modules/apache/__init__.py

@@ -55,7 +55,7 @@ class ApacheApp(app_module.App):
         self.add(freedombox_ports)
 
         letsencrypt = LetsEncrypt('letsencrypt-apache', domains='*',
-                                  daemons=['apache2'])
+                                  daemons=['apache2'], reload_daemons=True)
         self.add(letsencrypt)
 
         daemon = Daemon('daemon-apache', 'apache2')