Make two existing command line options "allow-suspicious-udfs" and
"skip-grant-tables" visible as global system variables.

Both options have security implications, but users were not able to check
their states in the server prior to this change. This was a security
issue, as the user may not be aware if the options are enabled. By adding
them into system variables, it increases users’ visibility into their
security configurations.

Create new MTR tests to verify that the system variables align with the
command line options. Minor adjustments to the existing MTR due to the new
members in system variables.

Before:
    mysql> SHOW VARIABLES WHERE
    Variable_Name LIKE 'allow_suspicious_udfs' OR
    Variable_Name LIKE 'skip_grant_tables';
    Empty set (0.000 sec)

After:
    mysql> SHOW VARIABLES WHERE
    Variable_Name LIKE 'allow_suspicious_udfs' OR
    Variable_Name LIKE 'skip_grant_tables';
    +-----------------------+-------+
    | Variable_name         | Value |
    +-----------------------+-------+
    | allow_suspicious_udfs | OFF   |
    | skip_grant_tables     | OFF   |
    +-----------------------+-------+

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.