Add IF EXISTS clause to DROP USER statement (ansible-collections#307)

* Add IF EXISTS clause to DROP USER statement

* Add a changelog fragment

* Fix exception

(cherry picked from commit 3a452fa)

changelogs/fragments/307-mysql_user_add_if_exists_to_drop.yml

@@ -0,0 +1,2 @@
+bugfixes:
+- "mysql_user - fix the possibility for a race condition that breaks certain (circular) replication configurations when ``DROP USER`` is executed on multiple nodes in the replica set. Adding ``IF EXISTS`` avoids the need to use ``sql_log_bin: no`` making the statement always replication safe (https://github.com/ansible-collections/community.mysql/pull/287)."

plugins/module_utils/user.py

@@ -419,7 +419,10 @@ def user_delete(cursor, user, host, host_all, check_mode):
         hostnames = [host]
 
     for hostname in hostnames:
-        cursor.execute("DROP USER %s@%s", (user, hostname))
+        try:
+            cursor.execute("DROP USER IF EXISTS %s@%s", (user, hostname))
+        except Exception:
+            cursor.execute("DROP USER %s@%s", (user, hostname))
 
     return True