hugo: create tempfiles in a dedicated temporary directory

Sometimes on testnodes hugo refuses to start because:

    Error: add site dependencies: create deps: failed to create file caches from configuration: mkdir /tmp/hugo_cache/default: permission denied
    Total in 0 ms
13 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:33

passed SlapOS.Eggs.UnitTest-Master.Python3

00:09:46

passed SlapOS.SlapRunner.ResilienceTest-Master

00:21:33

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:22:44

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

07:53:21

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

08:15:49

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:04:48

passed SlapOS.Eggs.UnitTest-Master.Python2

01:00:35

passed SlapOS.Eggs.UnitTest-Master.Python3

00:11:39

passed SlapOS.SlapRunner.ResilienceTest-Master

00:21:32

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:23:13

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

04:59:18

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

05:25:43