Changed installation method for MySQL 5.7.6 and later. Using 'mysqld --initialize' instead of deprecated mysql_install_db. Installation for earlier MySQL versions and MariaDB still use mysql_install_db.
Due to the above change, low_level_make_sandbox will now filter the "error" message in the output for the text '[Warning]'. If an "error" appears as warning, the installation is not halted.
Incompatible change: when using --force to install on top of an existing sandbox, the old data directory is copied to 'old_data' instead of being overwritten. This is due to the different behavior of 'mysqld --initialize' that does not support iintializing an existing data directory.
Added more tests. Improved a few of the existing ones.
Fixed test for user privileges that was broken in 5.7.6+