Explicitly close pipe end when we cease operations...

...because the other in-VM reference to that FD means that it won't
get GC'd after we release our local reference to the containing object,
and we wind up with the feeder end blocking on write to a still-fully-
open pipe rather than being made aware that the read end has needed
to shut down.

Bug 28756668

Change-Id: I90b6aaeaabe7d912d96d7ef57c24f68d87d9d0ab