With the goal of centralizing all tests in the system, this is a
first step to establish a Tests sub-tree. It will contain all of
the unit tests and test harnesses for the various components in the
system.
Right now, permission flags passed to VFS::open() are effectively ignored, but
that is going to change.
* O_RDONLY is 0, but it's still nicer to pass it explicitly
* POSIX says that binding a Unix socket to a symlink shall fail with EADDRINUSE
