test-acme-dns-tiny: fix subprocess.Popen argument list

3 jobs for v2-csr-argument in 32 minutes and 38 seconds (queued for 1 minute and 3 seconds)
Status Job ID Name Coverage
  Test
passed #348
jessie

00:11:03

90.0%
passed #349
jessie_backport

00:10:44

90.0%
passed #350
stretch

00:10:50

90.0%