ASTERIXDB-1205: fix union queries.

Fixed the AqlExpressionToPlanTranslator for union expression;
Eliminate shared operator references in translated logical plans;
Removed IntroduceUnionRule;
Fixed tuple source for SQL++ join clause;
Added regression tests.

Change-Id: Ib79a899ec4b35ece6f8f9f59b80126fed0c48851
Reviewed-on: https://asterix-gerrit.ics.uci.edu/629
Reviewed-by: Till Westmann <tillw@apache.org>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
diff --git a/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml b/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
index 2965883..d289400 100644
--- a/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
+++ b/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
@@ -1298,6 +1298,22 @@
             </compilation-unit>
         </test-case>
         <test-case FilePath="custord">
+            <compilation-unit name="join_q_05">
+                <output-dir compare="Text">join_q_01</output-dir>
+            </compilation-unit>
+        </test-case>
+        <test-case FilePath="custord">
+            <compilation-unit name="join_q_06">
+                <output-dir compare="Text">join_q_06</output-dir>
+            </compilation-unit>
+        </test-case>
+        <test-case FilePath="custord">
+            <compilation-unit name="join_q_07">
+                <output-dir compare="Text">join_q_06</output-dir>
+                 <expected-error>org.apache.hyracks.algebricks.common.exceptions.AlgebricksException: Could not resolve type for function-call: asterix:scan-collection, Args:[%0->$$8],please check whether the used variables has been defined!</expected-error>
+            </compilation-unit>
+        </test-case>
+        <test-case FilePath="custord">
             <compilation-unit name="load-test">
                 <output-dir compare="Text">load-test</output-dir>
             </compilation-unit>