This adds a new filter argument to the volume prune endpoint "all".
When this is not set, or it is a false-y value, then only anonymous
volumes are considered for pruning.
When `all` is set to a truth-y value, you get the old behavior.
This is an API change, but I think one that is what most people would
want.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
