BlockingIOError: [Errno 11] write could not complete without blocking

It seems that the new glibc-based runner is setting the remote-side of the communication pipes as non-blocking, which can lead to the following exception when plainbox cannot keep up with reading and parsing:

(job 2013.com.canonical.certification::udev_attachment, <stderr:00001>) Traceback (most recent call last):
  File "/tmp/nest-mz3t_nki.c18db61924f60c5a4f09dc8cd722329143c99a7f9a6cff4c3f6f90fc685b0df2/xml_sanitize", line 46, in <module>
    raise(err)
  File "/tmp/nest-mz3t_nki.c18db61924f60c5a4f09dc8cd722329143c99a7f9a6cff4c3f6f90fc685b0df2/xml_sanitize", line 43, in <module>
    sys.exit(main())
  File "/tmp/nest-mz3t_nki.c18db61924f60c5a4f09dc8cd722329143c99a7f9a6cff4c3f6f90fc685b0df2/xml_sanitize", line 39, in main
    print(text)
BlockingIOError: [Errno 11] write could not complete without blocking

This bug can be reproduced with: plainbox dev script 2013.com.canonical.certification::udev_attachment