Unittest - Try to avoid racing conditions failures when capturing stdout/stderr

* The new unblocking strategy for subprocesses involves timeouts and
waiting periods. If the timeout is too short (or absent) tests may show
intermittent failure.
* Increasing the timeout may make tests a bit slower but more reliable.
Merge pull request #8 in TM/task from ~UNODE/task:2.4.0 to 2.4.0

* commit '1f279ffde8e838a9cc34e2ebaa71200f0e0bb386':
  Unittest - Try to avoid racing conditions failures when capturing stdout/stderr