Post push fix for main.ps_ddl test case.

The test case uses a SHOW VARIABLES query that throws a warning when
displaying the content of the deprecated variable.

As the deprecated variable is not present on embedded servers, the same
test case do not throw warnings at SHOW VARIABLES.

The fix creates a new test include file to assert that no other warning
messages than the expected one (ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT)
were issued by the statement, making the test case result the same for
embedded and non-embedded servers.