Skip tests if the filesystem cannot support them

For example, when building on disorderfs we can't run the tests.
6 jobs for debian/master in 8 minutes and 17 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #204173
build

00:04:18

 
  Test
passed #204176
autopkgtest

00:03:21

passed #204177
blhc

00:01:36

passed #204175
lintian

00:02:15

passed #204178
piuparts

00:02:58

passed #204174
reprotest

00:03:58