build-sys: distribute testsuite

Fix 'make dist'
diff --git a/Makefile.am b/Makefile.am
index bd6ac4f..c611604 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -177,6 +177,8 @@
 testsuite_test_modprobe_LDADD = $(TESTSUITE_LDADD)
 testsuite_test_modprobe_CPPFLAGS = $(TESTSUITE_CPPFLAGS)
 
+EXTRA_DIST += testsuite/rootfs
+
 DISTCHECK_CONFIGURE_FLAGS=--enable-gtk-doc
 
 distclean-local: $(DISTCLEAN_LOCAL_HOOKS)