DISABLE AND ENABLED DURING DDL OPERATION

PROBLEM: Same thread trying to acquire the same mutex
         second time leads to hang/server crash.
         While [un]installing audit_log plugin
         a thread acquires the LOCK_plugin mutex
         and after successful initialization tries
         to write in mysql.plugin table. It holds
         this mutex for a long time. If some how
         plugin table is corrupted then a write to 
         plugin table will throw an error, thread try
         to log this error in the audit_log plugin,
         doing so it tries to acquire the mutex
         again and results is server hang/crash.

SOLUTION: Releasing the LOCK_plugin mutex before
          writing in mysql.plugin table. We dont
          need to hold this mutex as thread already
          acquired a TL_WRITE lock on mysql.plugin
          table.