ACT-1333 fixing upgrade script

modules/activiti-upgrade/src/test/resources/org/activiti/db/clean/clean.postgres.sql

-SELECT 
-  execute($$
-      drop table act_ge_property cascade
-  $$) 
-WHERE 
-  exists 
-  (
-    SELECT * 
-    FROM information_schema.tables 
-    WHERE table_name = 'act_ge_property'
-  );
-
-drop table if exists ACT_GE_BYTEARRAY cascade;
-drop table if exists ACT_RE_MODEL cascade;
-drop table if exists ACT_RE_DEPLOYMENT cascade;
-drop table if exists ACT_RE_PROCDEF cascade;
-drop table if exists ACT_RU_IDENTITYLINK cascade;
-drop table if exists ACT_RU_VARIABLE cascade;
-drop table if exists ACT_RU_TASK cascade;
-drop table if exists ACT_RU_EXECUTION cascade;
-drop table if exists ACT_RU_JOB cascade;
-drop table if exists ACT_RU_EVENT_SUBSCR cascade;
-drop table if exists ACT_HI_PROCINST cascade;
-drop table if exists ACT_HI_ACTINST cascade;
-drop table if exists ACT_HI_VARINST cascade;
-drop table if exists ACT_HI_TASKINST cascade;
-drop table if exists ACT_HI_DETAIL cascade;
-drop table if exists ACT_HI_COMMENT cascade;
-drop table if exists ACT_HI_ATTACHMENT cascade;
-drop table if exists ACT_ID_INFO cascade;
-drop table if exists ACT_ID_MEMBERSHIP cascade;
-drop table if exists ACT_ID_GROUP cascade;
-drop table if exists ACT_ID_USER cascade;