spacemanager: Delete flushed file reservations when name space entry is deteled

Space manager marks file reservations as deleted when the name space entry
is deleted. The actual file reservation is not removed until space manager
is notified that the file is removed from the pool. For files flushed to
tape there may not be a disk copy and thus such a notification is never sent.
The consequence is that reservations for flushed files are never removed.

This patch fixes the problem by deleting the file reservation of flushed files
as soon as the name space entry is deleted. A liquibase changeset is added to
delete old reservations for deleted flushed files.

Target: trunk
Require-notes: yes
Require-book: no
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Patch: http://rb.dcache.org/r/6435/