app_voicemail: Memory Leaks against tests

(issue ASTERISK-22467)
Reported by: Corey Farrell
Patches:
    app_voicemail-1.8.patch uploaded by coreyfarrell (license 5909)
    app_voicemail-11up.patch uploaded by coreyfarrell (license 5909)


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@401743 f38db490-d61c-443f-a65b-d21fe96a405b