fmf: Don't fail if we can't put selinux in permissive mode

The tests might be running unprivileged or in an environment without
selinux so let's not fail if we can't put it in permissive mode.

test/fmf/integration-tests/test.sh

@@ -4,8 +4,8 @@
 set -eux
 set -o pipefail
 
-# Switch SELinux to permissive, since the tests don't set proper contexts
-setenforce 0
+# Switch SELinux to permissive if possible, since the tests don't set proper contexts
+setenforce 0 || true
 
 # Allow running the integration tests downstream in dist-git with something like
 # the following snippet which makes the dist-git sources available in $TMT_SOURCE_DIR: