Adds MISC_SHARES_VIA_AGGREGATE standard trait

As discussed in Atlanta's PTG meetings, we will use the newly-added traits
functionality to mark a resource provider as providing shared resources to a
set of other resource providers. We need a new standard trait to represent this
shared provider characteristic, and this patch adds it
MISC_SHARES_VIA_AGGREGATE along with a fairly lengthy explanation of the
trait's meaning.

Change-Id: I4e9d8389c9b93ffee20adb53d864d55d335a27fd
blueprint: shared-resources-pike

os_traits/misc/__init__.py

@@ -0,0 +1,38 @@
+# -*- 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 = [
+    # Indicates that the resource provider decorated with this trait exposes
+    # its resources for consumption on *other* resource providers via an
+    # aggregate association. The canonical example here would be a shared
+    # storage pool.
+    #
+    # The deployer might create a resource provider, let's call it "NFS_SHARE"
+    # that has an inventory record of 2000 total DISK_GB resources.
+    #
+    # There may be 10 other resource providers, let's call them "CN_1" through
+    # "CN_10" that represent compute nodes. These compute node resource
+    # providers have inventory records for MEMORY_MB and VCPU resources, but no
+    # DISK_GB inventory.
+    #
+    # Both the "NFS_SHARE" resource provider and each of the "CN_x" resource
+    # providers are associated to the same aggregate, let's call it "AGG_A".
+    #
+    # Deployers would decorate the "NFS_SHARE" resource provider with the
+    # "MISC_SHARES_VIA_AGGREGATE" trait to indicate to the system that the
+    # DISK_GB inventory it provides can be consumed by consumers of resources
+    # on any of the other resource providers associated with any aggregate
+    # "NFS_SHARE" is associated to.
+    'SHARES_VIA_AGGREGATE',
+]

os_traits/tests/test_os_traits.py

@@ -36,6 +36,7 @@ class TestSymbols(base.TestCase):
         self.assertIn("HW_CPU_X86_AVX2", names)
         self.assertIn("STORAGE_DISK_SSD", names)
         self.assertIn("HW_NIC_SRIOV", names)
+        self.assertIn("MISC_SHARES_VIA_AGGREGATE", names)
 
     def test_get_traits(self):
         traits = ot.get_traits('HW_CPU')