-7 option needs to check if mysql is really 5.7

After documenting about -7 option, we also need to check if mysql is actually 5.7.

If unknowingly someone uses -7 option with mysql 5.5, it does not start because the variables we set are specific to 5.7

unknown variable 'slave_parallel_type=LOGICAL_CLOCK'

I was using this to check db version when its not running

mysql --version
mysql Ver 14.14 Distrib 5.5.52, for linux2.6 (x86_64) using EditLine wrapper

Start by locating the code that handles the -7 option and compare its behavior with the mysql --version output shown in the issue. Verify that MySQL 5.5 is not treated as 5.7, and confirm the option's behavior for supported and older versions.

Written by the indexing model from the issue text.