Remove resource used fields from ComputeNode

The node resource(vcpu, memory and disk) used infomation need
to change when creating or deleting instances. Now Placement do
not send notifications, so there is not a good way to capture
the change. We remove these fields and leave the process to strategy.

Partially Implements: blueprint improve-compute-data-model

Change-Id: I3f9a3279a26f3df444117d9265e74cca57b38d6e

watcher/tests/decision_engine/cluster/test_nova_cdmc.py

@@ -154,18 +154,12 @@ class TestNovaClusterDataModelCollector(base.TestCase):
 
         memory_total = (node.memory-node.memory_mb_reserved)*node.memory_ratio
         self.assertEqual(node.memory_mb_capacity, memory_total)
-        memory_free = memory_total - node.memory_mb_used
-        self.assertEqual(node.memory_mb_free, memory_free)
 
         disk_total = (node.disk_capacity-node.disk_gb_reserved)*node.disk_ratio
         self.assertEqual(node.disk_gb_capacity, disk_total)
-        disk_free = disk_total - node.disk_gb_used
-        self.assertEqual(node.disk_gb_free, disk_free)
 
         vcpus_total = (node.vcpus-node.vcpu_reserved)*node.vcpu_ratio
-        self.assertEqual(node.vcpus_capacity, vcpus_total)
-        vcpus_free = vcpus_total - node.vcpus_used
-        self.assertEqual(node.vcpus_free, vcpus_free)
+        self.assertEqual(node.vcpu_capacity, vcpus_total)
 
         m_nova_helper.get_compute_node_by_name.assert_called_once_with(
             minimal_node['hypervisor_hostname'], servers=True, detailed=True)