simplify BlockingProcessStreamReader; fix tests

[pongad]

Update #1429.

This commit simplifies the main run() method.
Previous implementation checks whether the underlying Reader is ready to read
then either reads a line or sleeps,
catching InterruptedException to watch for any thread interruption.

There are subtle difficulties with this approach:

• Even if the underlying Reader is ready to read, it might not have
  enough bytes to form a line. It might still block.
• It's not necessary to sleep. If the thread is interrupted while
  reading. It should throw InterruptedIOException.
  The method now reads in a loop, waiting for either exceptions or EOF.

The test class implements a mock Logger that logs to a data structure.
It then verifies that the data structure holds appropriate logs.
As implemented, this can cause a race, as two threads,
the writer and the verifier, run concurrently.
This commit fixes this by waiting for the writing thread to terminate
before verifying.

[coveralls]

Coverage decreased (-0.01%) to 83.577% when pulling fca0cfe on pongad:stream-reader into cacf65e on GoogleCloudPlatform:master.