Correction for some error message during asterisk restart

• lower the log level for loading moh to debug
• cherry-pick the fix(https://github.com/asterisk/asterisk/commit/c32d090e772e7e598732332a23a41109072413da) from asterisk project for the issue "Orphaned taskprocessors cause shutdown delays" https://github.com/asterisk/asterisk/issues/379

Please do not squash commits when merge, so we could keep the original commit from asterisk project.