duplicity builds but does not test

[Kenneth Loafman]

I'm getting some weird errors when building duplicity on 18.04-->19.10. The build finishes correctly but testing fails in odd ways. It all points to some sort of permission errors, mainly returning errno 1 for every spawn via subprocess.popen or pexpect. The executables are there, they have the correct permissions, etc.. Something about builder has changed. It's simply broken.

All tests pass when run under VBox VMs, except for 4 tests on Python 3.6. That's 2.7, 3.7, and 3.8 that perform properly.