BlockDevice -> DiskDevice.

BlockDevice was the wrong name for this abstraction, since a block device
is a type of file in a unix system, and we should use that name for that
concept in the fs implementation.

VirtualFileSystem/DiskDevice.cpp

@@ -0,0 +1,9 @@
+#include "DiskDevice.h"
+
+DiskDevice::DiskDevice()
+{
+}
+
+DiskDevice::~DiskDevice()
+{
+}