create_schema if auto-generate-sql also set.

mysqlslap uses a schema to run its tests on and later
drops it if auto-generate-sql is used. This can be a
problem, if the schema is an already existing one.

If create-schema is used with auto-generate-sql option,
mysqlslap while performing the cleanup, drops the specified
database.

Fixed by introducing an option --no-drop, which, if used,
will prevent the dropping of schema at the end of the test.


client/client_priv.h:
  Bug#11765157 - 58090: mysqlslap drops schema specified in
                 create_schema if auto-generate-sql also set.
  
  Added an option.
client/mysqlslap.c:
  Bug#11765157 - 58090: mysqlslap drops schema specified in
                 create_schema if auto-generate-sql also set.
  
  Introduced an option 'no-drop' to forbid the removal of schema
  even if 'create' or 'auto-generate-sql' options are used.
mysql-test/r/mysqlslap.result:
  Added a testcase for Bug#11765157.
mysql-test/t/mysqlslap.test:
  Added a testcase for Bug#11765157.