Move VFS from noux to 'os/include/vfs'

By separating the VFS from Noux, we become able to reuse the
VFS for libc-using programs. The most substantial change is the
removal of Noux::Sysio data structures from the VFS. Instead, the
Noux::Sysio refers to the VFS types now.

The new VFS library is located at 'os/include/vfs/'.

Furthermore, the patch removes various code duplications related
to pseudo file systems that provide a single file (block, zero,
random, terminal, null). The new 'Single_file_system' holds the
common boilerplate code for those.

Issue #999
vfs: LOG file system
vfs: ROM file system
vfs: inline file system
libc: Add fd status and flags to File_descriptor

Those values need to be stored local to the FD. Including
them in the 'File_descriptor' eases the handling of libc
plugins.
libc: Make File_descriptor::fd_path char const *
libc: Add 'rmdir' to plugin interface
libc_terminal: Use prio to override libc_vfs
libc_fs: Use priority higher than libc_vfs

This way, we make sure that libc_fs is used if both plugins are
present, which happens during the transition to libc_vfs.
fs test: Appropriately use rmdir instead of unlink
Add libc_vfs plugin and test

Issue #999
Retire libc_{log, block, fs, rom}

Those plugins are superseded by libc_vfs.

Issue #999
Merge libc_vfs plugin into libc

Issue #999
Unify success messages of run scripts

The pattern "Test succeeded" is relied on by the automated
testing framework. We need to use it consistently to avoid
false negatives.
base: check cpu_session pointer during destruction

Issue #1122
run: limit created threads in test

The rm_session quota of the context area is not sufficient to start more
then ~95 threads per address space. If one really needs so many threads per
address space one could increase the quota or dynamically respond to it using
the Expanding_rm_session class. Until now there is no need to support so much
threads per address space.

Issue #1122
os: Add 'Framebuffer::Session::sync_sigh'

The new framebuffer-session function allows a client to register a
handler for receiving display-synchronization events.
os: Make buffer size of 'Reporter' configurable
os: Refine Attached_rom_dataspace::update
os: Add Rect::contains() to geometry utils