#533: Partial implementation of disk system space reservation.

disk/DiskSystem.hpp

objectstore/cta.proto

scheduler/OStoreDB/OStoreDB.cpp

scheduler/OStoreDB/OStoreDB.hpp

scheduler/RetrieveMount.cpp

scheduler/RetrieveMount.hpp

scheduler/SchedulerDatabase.cpp

scheduler/SchedulerDatabase.hpp

scheduler/SchedulerDatabaseTest.cpp

...erver/castor/tape/tapeserver/daemon/DiskWriteTaskTest.cpp

...castor/tape/tapeserver/daemon/DiskWriteThreadPoolTest.cpp

.../castor/tape/tapeserver/daemon/RecallTaskInjectorTest.cpp