component/nxdtest: v↑ (namespaces, /tmp-on-tmpfs, cancellation)

This upgrade

- teaches nxdtest to run each testcase with its own /tmp and /dev/shm to
  detect after each test run leaked temporary files, leaked mount
  entries, to isolate different test runs from each other, and to provide
  tmpfs on /tmp for every test.

  nxdtest!13

- teaches nxdtest to propagate cancellation to spawned test jobs, so
  that whenever user cancels corresponding test run in ERP5 UI, nxdtest
  stops promptly. This should be most useful for long-running tests like
  SlapOS.SoftwareReleases.IntegrationTest-* which before had to be
  waited for for hours to complete even after cancelling test run in ERP5.

  nxdtest!14

Pytest-mock is added because it becomes dependency to test nxdtest
itself.

component/nxdtest/buildout.cfg

@@ -48,6 +48,6 @@ depends = ${python-prctl:egg}
 [nxdtest-repository]
 recipe  = slapos.recipe.build:gitclone
 repository = https://lab.nexedi.com/nexedi/nxdtest.git
-revision = 9f413221
+revision = 81b1907a
 location = ${buildout:parts-directory}/nxdtest
 git-executable = ${git:location}/bin/git

component/pytest/buildout.cfg

@@ -16,3 +16,4 @@ eggs    = ${pytest:eggs}
 [versions]
 pytest  = 4.6.11:whl
 pytest-timeout = 1.4.2
+pytest-mock = 2.0.0:whl