polkit: Tweak policy to work for Cockpit

By installing our own rules while testing.

Signed-off-by: Stef Walter <stefw@redhat.com>
 - These are for our tests, we won't install these on systems
daemon: Run usermod via pkexec

So that admins can change roles and password hashes of user accounts.

Reviewed-by: Stef Walter <stefw@redhat.com>
daemon: Perform systemd actions via pkexec and systemctl

Instead of via D-Bus methods.  This enables admins to start/stop/etc
services.

Reviewed-by: Stef Walter <stefw@redhat.com>
test: Run more tests as "admin"

Fixes #1203
Fixes #1204
Fixes #1206
Closes #1238
Signed-off-by: Stef Walter <stefw@redhat.com>
 - Removed rules.d from main Cockpit package