When the `discard-recording` flag is given in one of the commands to
rtpengine (e.g. in the `delete` command), the metafile is renamed to a
.DISCARD suffix and then deleted.
The recording daemon then, seeing the .DISCARD suffix, proceeds to
immediately close all recordings, delete the files if any, and delete
the entries from the DB.
Change-Id: I3f0cac129f2d56cbccd770d43bf434dea6c0a0db