fmf: Plumb through $TEST_* variables for unexpected messages

This will allow us to control the value from test plans, in particular
for disabling at least some unexpected message checks for reverse
dependency testing. We don't want to disable unexpected messages
in general for fmf, as we are looking for exactly these in e.g.
selinux-policy reverse dependency tests.

Move from `su` to `runtest`, as with the former it's impossible to plumb
through variables with non-trivial characters, as they cannot be quoted.

Taken from cockpit-project/cockpit-podman@c38692fa4ce66

plans/all.fmf

@@ -7,6 +7,10 @@ discover:
 execute:
     how: tmt
 
+# Let's handle them upstream only, don't break Fedora/RHEL reverse dependency gating
+environment:
+    TEST_AUDIT_NO_SELINUX: 1
+
 /basic:
     summary: Run tests for basic packages
     discover+:

test/browser/browser.sh

@@ -5,10 +5,13 @@ set -eux
 # like "basic", passed on to run-test.sh
 PLAN="$1"
 
+export TEST_BROWSER=${TEST_BROWSER:-firefox}
+
 MYDIR="$(realpath $(dirname "$0"))"
 SOURCE="$(realpath $MYDIR/../..)"
 # https://tmt.readthedocs.io/en/stable/overview.html#variables
 LOGS="${TMT_TEST_DATA:-$(pwd)/logs}"
+export SOURCE LOGS
 mkdir -p "$LOGS"
 chmod a+w "$LOGS"
 
@@ -84,7 +87,9 @@ firewall-cmd --add-service=cockpit --permanent
 firewall-cmd --add-service=cockpit
 
 # Run tests as unprivileged user
-su - -c "env TEST_BROWSER=firefox SOURCE=$SOURCE LOGS=$LOGS $MYDIR/run-test.sh $PLAN" runtest
+# once we drop support for RHEL 8, use this:
+# runuser -u runtest --whitelist-environment=TEST_BROWSER,TEST_ALLOW_JOURNAL_MESSAGES,TEST_AUDIT_NO_SELINUX,SOURCE,LOGS "$MYDIR/run-test.sh" "$PLAN"
+runuser -u runtest --preserve-environment env USER=runtest HOME="$(getent passwd runtest | cut -f6 -d:)" "$MYDIR/run-test.sh" "$PLAN"
 
 RC=$(cat $LOGS/exitcode)
 exit ${RC:-1}

test/browser/run-test.sh

@@ -62,6 +62,11 @@ export TEST_ALLOW_JOURNAL_MESSAGES
 TESTS=""
 EXCLUDES=""
 RC=0
+
+# make it easy to check in logs
+echo "TEST_ALLOW_JOURNAL_MESSAGES: ${TEST_ALLOW_JOURNAL_MESSAGES:-}"
+echo "TEST_AUDIT_NO_SELINUX: ${TEST_AUDIT_NO_SELINUX:-}"
+
 if [ "$PLAN" = "optional" ]; then
     TESTS="$TESTS
            TestAutoUpdates