fmf: Force SELinux relabel when running within testing farm

We expect to run as root within testing farm and to have permissions
to do selinux relabelling so let's enable it explicitly.

test/fmf/integration-tests/test.sh

@@ -78,6 +78,9 @@ fi
 
 if [[ -n "${TESTING_FARM_REQUEST_ID:-}" ]]; then
     tee --append mkosi.local.conf <<EOF
+[Content]
+SELinuxRelabel=yes
+
 [Build]
 ToolsTreeSandboxTrees=
         /etc/yum.repos.d/:/etc/yum.repos.d/