Make test_unmount usable in cleanup subroutines

- Duplicate test_unmount to _test_unmount
- Remove atf_check calls
- Call _test_unmount from test_unmount, checking the exit code
  at the end, and returning it to maintain the test_unmount
  "contract"

MFC after:	1 week

contrib/netbsd-tests/fs/tmpfs/h_funcs.subr

@@ -59,12 +59,31 @@ test_mount() {
 #	Unmounts the file system mounted by test_mount.
 #
 test_unmount() {
+	# Begin FreeBSD
+	_test_unmount
+	exit_code=$?
+	atf_check_equal "$exit_code" "0"
+	return $exit_code
+	# End FreeBSD
 	cd - >/dev/null
 	atf_check -s eq:0 -o empty -e empty umount ${Mount_Point}
 	atf_check -s eq:0 -o empty -e empty rmdir ${Mount_Point}
 	Mount_Point=
 }
 
+# Begin FreeBSD
+_test_unmount() {
+	if [ -z "${Mount_Point}" -o ! -d "${Mount_Point}" ]; then
+		return 0
+	fi
+
+	cd - >/dev/null
+	umount ${Mount_Point}
+	rmdir ${Mount_Point}
+	Mount_Point=
+}
+# End FreeBSD
+
 #
 # kqueue_monitor expected_nevents file1 [.. fileN]
 #