File terminal is a service that provides a terminal-session interface and
redirects the terminal input and output to a file.

! <config>
!   <policy label_prefix="client1" filename="test.txt"/>
!   <policy label_prefix="client2" filename="file.dat" io_buffer_size="4K"/>
!   <libc stdout="/dev/log"/>
!   <vfs>
!     <dir name="dev"> <log/> </dir>
!     <fs/>
!   </vfs>
! </config>

To keep things simple, a client can only open one file at the moment.
