Fix a bug that Mroonga_log_level variable value can't be set in my.cnf
Fix a bug that Mroonga_log_level variable value can't be set in my.cnf

[groonga-dev,01379]

Reported by Kazuhiro Isobe. Thanks!!!

yoku0825/mroonga,naoa/mroonga,mroonga/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,naoa/mroonga