xdist munges error message if a requested path does not exist

Using code in this branch: https://github.com/nexB/scancode-toolkit/pull/414 calling py.test on a non-existing path does not return an error message with xdist, it just runs no tests:

(scancode-toolkit) pombreda@COMPUTER:~/w421/scancode-toolkit$ py.test -vvs -n 2 MISSING
========================================================================== test session starts ==========================================================================
platform linux2 -- Python 2.7.6, pytest-3.0.5, py-1.4.32, pluggy-0.4.0 -- /home/pombreda/w421/scancode-toolkit/bin/python2.7
cachedir: .cache
rootdir: /home/pombreda/w421/scancode-toolkit, inifile: setup.cfg
plugins: xdist-1.15.0
[gw0] linux2 Python 2.7.6 cwd: /home/pombreda/w421/scancode-toolkit
[gw1] linux2 Python 2.7.6 cwd: /home/pombreda/w421/scancode-toolkit
[gw0] Python 2.7.6 (default, Oct 26 2016, 20:30:19)  -- [GCC 4.8.4]
[gw1] Python 2.7.6 (default, Oct 26 2016, 20:30:19)  -- [GCC 4.8.4]
gw0 [0] / gw1 [0]
scheduling tests via LoadScheduling

===================================================================== no tests ran in 0.30 seconds ======================================================================

In contrast without xdist, it does print alright: ERROR: file not found: MISSING

(scancode-toolkit) pombreda@COMPUTER:~/w421/scancode-toolkit$ py.test -vvs  MISSING
========================================================================== test session starts ==========================================================================
platform linux2 -- Python 2.7.6, pytest-3.0.5, py-1.4.32, pluggy-0.4.0 -- /home/pombreda/w421/scancode-toolkit/bin/python2.7
cachedir: .cache
rootdir: /home/pombreda/w421/scancode-toolkit, inifile: setup.cfg
plugins: xdist-1.15.0

===================================================================== no tests ran in 0.00 seconds ======================================================================
ERROR: file not found: MISSING