Revert "[autotest] Remove unnecessary tko/db construction logic"

This reverts commit 027561f6e13704357744b035917284f44b3de1b7.

Reason for revert: https://crbug.com/860166

Original change's description:
> [autotest] Remove unnecessary tko/db construction logic
> 
> There was exactly one db_type implemented but we were redirecting via
> some string formatted imports to get to it. Yuck.
> 
> Also, implementing logic via magic functions implemented in subclasses
> is bad.
> 
> BUG=chromium:852083
> TEST=pre-cq passes.
> 
> Change-Id: I5029cbe63e2c4e8d093f3776848fff83103e75df
> Reviewed-on: https://chromium-review.googlesource.com/1123026
> Commit-Ready: Prathmesh Prabhu <pprabhu@chromium.org>
> Tested-by: Aviv Keshet <akeshet@chromium.org>
> Reviewed-by: Aviv Keshet <akeshet@chromium.org>

Bug: chromium:852083
Change-Id: I5d376dd7ff1903e36c5085955285b4810c1a494a
Reviewed-on: https://chromium-review.googlesource.com/1126419
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Commit-Queue: Jason Clinton <jclinton@chromium.org>
Tested-by: Jason Clinton <jclinton@chromium.org>
Trybot-Ready: Jason Clinton <jclinton@chromium.org>
diff --git a/tko/db_mysql.py b/tko/db_mysql.py
new file mode 100644
index 0000000..02b1e96
--- /dev/null
+++ b/tko/db_mysql.py
@@ -0,0 +1,19 @@
+import common
+import MySQLdb as driver
+import db
+from autotest_lib.client.common_lib.cros import retry
+
+class db_mysql(db.db_sql):
+    @retry.retry(db._get_error_class("OperationalError"), timeout_min=10,
+                 delay_sec=5)
+    def connect(self, host, database, user, password, port):
+        connection_args = {
+            'host': host,
+            'user': user,
+            'db': database,
+            'passwd': password,
+            'connect_timeout': 20,
+        }
+        if port:
+            connection_args['port'] = int(port)
+        return driver.connect(**connection_args)