[Core] Add Red.wait_until_red_ready() function to wait until post connection startup is done (#3273)

* enhance: add `Red.wait_until_red_ready()` for post connection startup

* enhance: fill `bot.owner_id` in our `on_ready`

* enhance: log missing destinations in `get_owner_notification_destinations`

* chore(changelog): add towncrier entries

* chore(changelog): use past form of verb "add"

redbot/core/events.py

@@ -48,9 +48,12 @@ def init_events(bot, cli_flags):
         guilds = len(bot.guilds)
         users = len(set([m for m in bot.get_all_members()]))
 
+        app_info = await bot.application_info()
+        if bot.owner_id is None:
+            bot.owner_id = app_info.owner.id
+
         try:
-            data = await bot.application_info()
-            invite_url = discord.utils.oauth_url(data.id)
+            invite_url = discord.utils.oauth_url(app_info.id)
         except:
             invite_url = "Could not fetch invite url"
 
@@ -75,6 +78,7 @@ def init_events(bot, cli_flags):
 
         INFO.append("{} cogs with {} commands".format(len(bot.cogs), len(bot.commands)))
 
+        outdated_red_message = ""
         with contextlib.suppress(aiohttp.ClientError, discord.HTTPException):
             async with aiohttp.ClientSession() as session:
                 async with session.get("https://pypi.python.org/pypi/red-discordbot/json") as r:
@@ -84,13 +88,10 @@ def init_events(bot, cli_flags):
                     "Outdated version! {} is available "
                     "but you're using {}".format(data["info"]["version"], red_version)
                 )
-
-                await bot.send_to_owners(
+                outdated_red_message = (
                     "Your Red instance is out of date! {} is the current "
-                    "version, however you are using {}!".format(
-                        data["info"]["version"], red_version
-                    )
-                )
+                    "version, however you are using {}!"
+                ).format(data["info"]["version"], red_version)
         INFO2 = []
 
         reqs_installed = {"docs": None, "test": None}
@@ -123,6 +124,9 @@ def init_events(bot, cli_flags):
             print("\nInvite URL: {}\n".format(invite_url))
 
         bot._color = discord.Colour(await bot._config.color())
+        bot._red_ready.set()
+        if outdated_red_message:
+            await bot.send_to_owners(outdated_red_message)
 
     @bot.event
     async def on_command_error(ctx, error, unhandled_by_cog=False):