ptest-runner: Pull in parallel test fixes and output handling

Pull in the commits:

    Flush stdout and stderr after test
    Remove _child_reader singleton
    Report test failure on timeout
    Only collect system state on timeout
    Revert "Change test timeout to be total elapsed time"
    Change test timeout to be total elapsed time
    Report if child dies from a signal
    Recreate pipe for each test
    Revert "runner: Correctly handle running parallel tests"
    runner: Correctly handle running parallel tests

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 8de47e5f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>