Problem:
=======

Server refuses to startup when innodb_force_recovery > 3 and
InnoDB making the server to read-only mode before applying the redo log.

Solution:
========
Introduce a new variable called high_level_read_only and
it will be enabled when server is in read-only mode or
innodb_force_recovery > 3. This variable will be
checked during DML and DDL(expect Drop table). In other words,
Drop table is the only operation allowed when innodb_force_recovery > 3.

Reviewed-by: Marko Mäkelä <marko.makela@oracle.com>
RB: 9320