Problem: "read-only" option ignored if it's enabled in
the command line (or in the config file).

Fix: sync opt_readonly (which is used for checks) with 
read_only (global var) when all server options are handled.


mysql-test/r/bug58669.result:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - test result.
mysql-test/t/bug58669-master.opt:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - test case.
mysql-test/t/bug58669.test:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - test case.
sql/mysqld.cc:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - sync opt_readonly boolean with read_only boolean
  in the get_options().
sql/mysqld.h:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - sync opt_readonly boolean with read_only boolean
  in the get_options().
sql/sys_vars.cc:
  Fix for bug #58669: read_only not enforced on 5.5.x
    - sync opt_readonly boolean with read_only boolean
  in the get_options().