build: distribute TAP helper scripts in tarballs

Signed-off-by: Simon McVittie <smcv@debian.org>

Closes: #337
Approved by: cgwalters

Makefile-tests.am

@@ -19,6 +19,11 @@
 
 include $(top_srcdir)/buildutil/glib-tap.mk
 
+EXTRA_DIST += \
+	buildutil/tap-driver.sh \
+	buildutil/tap-test \
+	$(NULL)
+
 # We should probably consider flipping the default for DEBUG.  Also,
 # include the builddir in $PATH so we find our just-built ostree
 # binary.