Add a counter to the 'database deltree' CLI command.

Note: this is slightly different than the initial patch, because I felt
 that using res <= 0 would be a change in behavior.

Closes issue #10687, patch by junky


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@82154 65c4cc65-6c06-0410-ace0-fbb531ad65f3