core: bring manager_startup() and manager_reload() more inline

core: bring manager_startup() and manager_reload() more inline

Both functions do partly the same, let's make sure they do it in the
same order, and that we don't miss some calls.

This makes a number of changes:

1. Moves exec_runtime_vacuum() two calls down in manager_startup(). This
   should not have any effect but makes manager_startup() more like
   manager_reload().

2. Calls manager_recheck_journal(), manager_recheck_dbus(),
   manager_enqueue_sync_bus_names() in manager_startup() too. This is a
   good idea since during reeexec we pass through manager_startup() and
   hence can't assume dbus and journald weren't up yet, hence let's
   check if they are ready to be connected to.

3. Include manager_enumerate_perpetual() in manager_reload(), too. This
   is not strictly necessary, since these units are included in the
   serialization anyway, but it's still a nice thing, in particular as
   theoretically the deserialization could fail.