Run a variable value checks when setting it with 'set persist_only'

It must not be allowed to execute invalid values of default_table_encryption with PERSIST_ONLY.
For instance:
mysql> set global default_table_encryption=-1;
ERROR 1231 (42000): Variable 'default_table_encryption' can't be set to the value of '-1'

However, if we execute this with PERSIST only
mysql> set persist_only default_table_encryption=-1;
Query OK, 0 rows affected (0.00 sec)

This will cause a problem during server restart. Because the execution of the above command creates an entry in mysqld_auto.cnf file and the server fails to start as the value -1 is invalid.

The fix should be similar to other variables like, for eg
mysql> set global autocommit=-1;
ERROR 1231 (42000): Variable 'autocommit' can't be set to the value of '-1'
mysql> set persist_only autocommit=-1;
ERROR 1231 (42000): Variable 'autocommit' can't be set to the value of '-1'
mysql> set persist autocommit=-1;