Fix remote submix crash on null sink

Fix remote submix crash on null sink

The "remote submix" HAL uses a MonoPipe instance to "pipe" audio
  from the sink of this virtual device HAL to its source.
  The life-cycle of this pipe is:
  - creation when either the input or output stream is open
  - destruction when both input and output are closed.

Changes are:
Fix test for pipe destruction: destroy pipe when both
  input and output streams are NULL.
Count how many read errors went into the logs and cap them
  so as not to spam the logs when the pipe is not properly
  set up. Less 'I' logs, 'D' logs instead.
When opening input stream, check for non-null sink before
  checking if it's shutdown.

Bug 16653334
Bug 17111907

Change-Id: I634b4192b00f9b74a5109f42242423e9c8cb4c7c