Apply interruptible sleep to slow devices

[cahirwpz]

Part of pipe and tty read / write semantics is that they can be interrupted. An excerpt from Linux's signal(7) follows:

If a blocked call to one of the following interfaces is interrupted by a signal handler, then the call is automatically restarted after the signal handler returns if the SA_RESTART flag was used; otherwise the call fails with the error EINTR:

• read(2), readv(2), write(2), writev(2), and ioctl(2) calls on "slow" devices. A "slow" device is one where the I/O call may block for an indefinite time, for example, a terminal, pipe, or socket. If an I/O call on a slow device has already transferred some data by the time it is interrupted by a signal handler, then the call will return a success status (normally, the number of bytes transferred). Note that a (local) disk is not a slow device according to this definition; I/O operations on disk devices are not interrupted by signals.
• open(2), if it can block (e.g., when opening a FIFO; see fifo(7)).
• wait(2), wait3(2), wait4(2), waitid(2), and waitpid(2).
  ...

[jpszczolowski]

I see that interruptible sleep has been implemented by @ilikeheaps in #450 #460 #462
AFAIU currently we have 3 methods:

• cv_wait (uninterruptible),
• cv_wait_intr (interruptible, no timeout),
• cv_wait_timed (interruptible, timeout).