ash: add all hush parsing tests to ast tests

All pass.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-parsing/process_subst.right b/shell/ash_test/ash-parsing/process_subst.right
new file mode 100644
index 0000000..397bc80
--- /dev/null
+++ b/shell/ash_test/ash-parsing/process_subst.right
@@ -0,0 +1,3 @@
+TESTzzBEST
+TEST$(echo zz)BEST
+TEST'BEST