Fix mysql connection errror on boot

Mysql triggers "Host 'xxx' is not allowed to connect to this MySQL
server" error because of race condition.

This was an issue that had been (painfully) solved in v2 and has reared
its ugly head again in v3.

Close #159
Close #160

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Latest
 
+- [Bugfix] fix mysql initialization (#156, #160)
 - [Improvement] Better handling of continuous integration
 - [Bugfix] fix `tutor --version` (#156)
 - [Improvement] Absolute settings imports -- 📯 thanks @tonytan4ever!

tutor/local.py

@@ -1,4 +1,5 @@
 import os
+import subprocess
 from time import sleep
 
 import click
@@ -130,16 +131,26 @@ def run(root, service, command, args):
 )
 @opts.root
 def databases(root):
+    init_mysql(root)
+    ops.migrate(root, run_bash)
+
+def init_mysql(root):
     mysql_data_path = tutor_env.data_path(root, "mysql", "mysql")
-    if not os.path.exists(mysql_data_path):
+    if os.path.exists(mysql_data_path):
+        return
     click.echo(fmt.info("Initializing MySQL database..."))
     docker_compose(root, "up", "-d", "mysql")
-        while not os.path.exists(mysql_data_path):
-            click.echo(fmt.info("    waiting for creation of {}".format(mysql_data_path)))
-            sleep(4)
+    while True:
+        click.echo(fmt.info("    waiting for mysql initialization"))
+        logs = subprocess.check_output([
+            "docker-compose", "-f", tutor_env.pathjoin(root, "local", "docker-compose.yml"),
+            "logs", "mysql",
+        ])
+        if b"MySQL init process done. Ready for start up." in logs:
             click.echo(fmt.info("MySQL database initialized"))
             docker_compose(root, "stop", "mysql")
-    ops.migrate(root, run_bash)
+            return
+        sleep(4)
 
 @click.group(help="Manage https certificates")
 def https():