Add COMPUTE_STATUS_DISABLED trait

This will be used by nova to signal when a compute node
resource provider is disabled so that a placement request
pre-filter in the nova scheduler can ask placement to filter
out compute node allocation candidates that are disabled,
similar to the post-placement ComputeFilter.

Part of nova blueprint pre-filter-disabled-computes

Change-Id: Ia8e4487bfb59f764a6817ec8650785ffa902eab5

os_traits/compute/status.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+TRAITS = [
+    # The compute node resource provider is disabled.
+    'DISABLED',
+]