Post push fix for BUG#91480 fixing autotest downgrade failures
by initializing the mysql server using --init-file with configuration
file enabling root connection from any host for mysql-5.7 and onwards
versions.

Adds logic to setup_files, to call a method "generate_init_file_configuration"
which generates "mysql-init-file.sql" and writes the sql statement to rename
the user from root@localhost to root@%, and passes the file with mysqld during
initialization of DB. This causes the mysql server to allow connections from
"root" users of any host.

Applying this solution only to mysql-5.7 and onwards versions, since Mysql-5.6
and mysql-5.5 versions, uses mysql_install_db script since mysqld doesnt support
"--initialize-insecure" for initialization.

The fix made earlier didnt resolve the issue with remote connections. This is
due to the default configuration of mysql server causing it to accept the
connections from local host only.