[FT] ncat process do not provide information, if any, about the error during execution

[Rodolfo Alonso]

Sometimes "ncat" do not start correctly. The test case exits with this exception:
RuntimeError: Process ['ncat', '0.0.0.0', '1234', '-l', '-k'] hasn't been spawned in 20 seconds

I could be very useful to retrieve the stderr and stdout pipes from the process, if any, to figure out why a simple process like ncat didn't start.

Logs:
https://storage.bhs.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_58c/704376/5/check/neutron-functional/58c2e19/testr_results.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/705065

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/705065
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=97773eaea6407eb12a0f1a2b8dbac24a71f3b7c6
Submitter: Zuul
Branch: master

commit 97773eaea6407eb12a0f1a2b8dbac24a71f3b7c6
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Thu Jan 30 16:58:12 2020 +0000

    Increase log information when a RootHelperProcess fails

    If a RootHelperProcess does not start, add more information to the
    exception raised: the command return code, the stdout and the stderr.

    Change-Id: I229e926341c5e6c8b06f59950e3ae09864d0f1f6
    Closes-Bug: #1861221

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 16.0.0.0b1 development milestone.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/train
Review: https://review.opendev.org/721695

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/721695
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=b1811dc1bb59661cc18c83812035dca69453f1da
Submitter: Zuul
Branch: stable/train

commit b1811dc1bb59661cc18c83812035dca69453f1da
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Thu Jan 30 16:58:12 2020 +0000

    Increase log information when a RootHelperProcess fails

    If a RootHelperProcess does not start, add more information to the
    exception raised: the command return code, the stdout and the stderr.

    Change-Id: I229e926341c5e6c8b06f59950e3ae09864d0f1f6
    Closes-Bug: #1861221
    (cherry picked from commit 97773eaea6407eb12a0f1a2b8dbac24a71f3b7c6)