This sometimes fails, since months, and nobody has fixed it.
Let's improve the reliability of CI a bit.

Change-Id: Ic4d2e085151855d35804f8ed6ebca04366815c0b
Reviewed-on: https://gerrit.libreoffice.org/49144Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>