Remove default node group.

In this way, CREATE DATASET statement can adjust to dynamic
cluster topology.

When we create a dataset:
- if the node group name is not given, we create a new node group
  using all currently available nodes;
- if the node group name is give, we use the given node group for
  the dataset.

When we drop a dataset:
- if no other dataset depends on the node group of the dataset to
  be dropped, we also drop the node group.

Change-Id: If68dc6a7c1270ab1f5049c9334e3318425fd8287
Reviewed-on: https://asterix-gerrit.ics.uci.edu/1799
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
BAD: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Michael Blow <mblow@apache.org>
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
index f9ae2fa..4574c66 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
@@ -3192,6 +3192,11 @@
       </compilation-unit>
     </test-case>
     <test-case FilePath="misc">
+      <compilation-unit name="dataset_nodegroup">
+        <output-dir compare="Text">dataset_nodegroup</output-dir>
+      </compilation-unit>
+    </test-case>
+    <test-case FilePath="misc">
       <compilation-unit name="partition-by-nonexistent-field">
         <output-dir compare="Text">partition-by-nonexistent-field</output-dir>
         <expected-error>Field "id" is not found</expected-error>