A custom config file written with tee gets the server umask. With umask
027 or 077 the file is not readable by the container user, so MySQL and
MariaDB ignored the whole config without an error.
- Set mode 644 on the MySQL, MariaDB, PostgreSQL, and MongoDB custom
config files after each write.
- Close the multiplexed SSH connection when the server user, IP, or port
changes, so the next command does not run as the old user.
Closes#11600
