Added deprecation notice for MySQL-Sandbox.

More compatibility options for MySQL 8.0.4

Added backward compatibility options for authentication plugin
in MySQL 8.0.4.
The default authentication was changed from
mysql_native_password to caching_sha2_password
To keep the new default, use --keep_auth_plugin.

Adapted MySQL-Sandbox to new default users

- Changed grants to support new users changes in 5.7.19 and 8.0.4
  (mysql.session, mysql.infoschema)
- Improved tests to deal with new default users

Maintenance release

- Added a conditional delay in ./use, as a temporary workaround for
  changed replication defaults in MySQL 8.0.x.
- Added a global check to stop operations if ~/.mylogin.cnf is detected

Updated --expose_dd_tables procedure to deal with DD changes in 8.0.2

Changed initial check for system tables: MySQL 8.0.2 has a tablespace…

… instead

Removed "--socket" from mysqlsh script

Fixed error in --custom_mysqld handling

updated MANIFEST

Added option --expose_dd_tables

The new option allow you to show and use MySQL 8.0
data dictionary hidden tables.
It requires mysqld-debug to be available