tests: adapt tearDown() method for classes so they correctly cleanup temporary files

3 jobs for v2.1-acme-draft-16 in 9 minutes and 37 seconds (queued for 28 seconds)
Status Job ID Name Coverage
  Test
passed #458
jessie

00:03:12

88.0%
passed #459
jessie_backport

00:03:06

88.0%
passed #460
stretch

00:03:18

88.0%