kes Rework next_vol and autoprune a bit due to failure in

kes  Rework next_vol and autoprune a bit due to failure in
     recycle-test.  prune_volumes() now returns no status,
     but should prune at least one Volume, if possible.
kes  Modify check_if_volume_valid_or_recyclable to reject a
     volume with Recycle set off.
kes  Modify prune_volumes() to continue if volume Recycle is off
     or if the volume has expired. Add more debug.

git-svn-id: https://bacula.svn.sourceforge.net/svnroot/bacula/trunk@7939 91ce42f0-d328-0410-95d8-f526ca767f89