[Audio] V3/auto autostart only (#1420)

* Download jar at audio load

* Messy...

* Remove leftover log file stuff

* Keep application.yml

* Damn you windows

redbot/cogs/audio/manager.py

@@ -0,0 +1,41 @@
+import shlex
+import asyncio
+from subprocess import Popen, DEVNULL
+import os
+
+proc = None
+SHUTDOWN = asyncio.Event()
+
+
+async def monitor_lavalink_server(loop):
+    while not SHUTDOWN.is_set():
+        if proc.poll() is not None:
+            break
+        await asyncio.sleep(0.5)
+
+    if not SHUTDOWN.is_set():
+        print("Lavalink jar shutdown, restarting.")
+        await start_lavalink_server(loop)
+
+
+async def start_lavalink_server(loop):
+    from . import LAVALINK_DOWNLOAD_DIR, LAVALINK_JAR_FILE
+    start_cmd = "java -jar {}".format(LAVALINK_JAR_FILE.resolve())
+
+    global proc
+    proc = Popen(
+        shlex.split(start_cmd, posix=os.name == 'posix'),
+        cwd=str(LAVALINK_DOWNLOAD_DIR),
+        stdout=DEVNULL, stderr=DEVNULL
+    )
+
+    print("Lavalink jar started. PID: {}".format(proc.pid))
+
+    loop.create_task(monitor_lavalink_server(loop))
+
+
+def shutdown_lavalink_server():
+    print("Shutting down lavalink server.")
+    SHUTDOWN.set()
+    if proc is not None:
+        proc.terminate()