[toranj] add partition id set/get to test-001-get-set (#3998)

tests/toranj/test-001-get-set.py

@@ -176,8 +176,14 @@ all_gettable_props = [
 
 all_posix_app_gettable_props = [wpan.WPAN_RCP_VERSION]
 
+# note: partitionid only takes effect after forming one Thread network.
+node.set(wpan.WPAN_PARTITION_ID, '12345678')
+
 node.form('get-set')
 
+# verify that partitionid property is indeed changed.
+verify(int(node.get(wpan.WPAN_PARTITION_ID), 0) == 12345678)
+
 for prop in all_gettable_props:
     node.get(prop)