test: Add support for teardown in tests

If a test defines a function 'test_teardown(), that function will be
called before the test env teardown is run.

Signed-off-by: Magnus Malm <magnusmalm@gmail.com>

test/lib.sh

@@ -69,6 +69,11 @@ say() {
 
 teardown() {
     test_status="$?"
+
+    if type test_teardown > /dev/null 2>&1 ; then
+	test_teardown
+    fi
+
     log "$color_reset" '--' ''
     if [ "$test_status" -eq 0 ]; then
         log "$fg_green" 'TEST PASS' ''