single quotes or syntax errors in Test-Command cause looping runs

[Iain Lane]

lua-torch-sys has Test-Command: luajit -lsys -e 'print(true)'. This breaks autopkgtest like so:

Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: autopkgtest [12:49:52]: test command1: luajit -lsys -e 'print(true)'
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: autopkgtest [12:49:52]: test command1: [-----------------------
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: bash: -c: line 0: syntax error near unexpected token `('
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: bash: -c: line 0: `set -e; export USER=`id -nu`; . /etc/profile >/dev/null 2>&1 || true; . ~/.profile >/dev/null 2>&1 || true;
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: autopkgtest [12:49:52]: test command1: -----------------------]
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: sh: 1: cannot open /tmp/autopkgtest.YPL5MU/command1-stdout: No such file
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: Exit request sent.
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: Creating nova instance adt-artful-amd64-lua-torch-sys-20170729-122728 from image ubuntu/ubuntu-artful-adt-amd64-server-20170729.
Jul 29 12:50:54 juju-prod-ues-proposed-migration-machine-3 sh[24958]: <VirtSubproc>: failure: copyup source failed, status 2

Replacing that with a " fixes things, but that sucks - it's not clear why that is required.

I also think that we shouldn't tempfail in this case since it's not going to get better.