Add COMPUTE_IMAGE_TYPE_* traits

These are traits used to represent Glance image types that may be supported
by a service such as nova-compute. Glance defines these types rigidly in
their documentation:

  https://docs.openstack.org/image-guide/image-formats.html#disk-formats

and thus they should be stable and standardized for use in placement
queries.

Change-Id: I2a76e6b1062b0112faec73cef4a369124e45aa98

os_traits/compute/image.py

@@ -0,0 +1,39 @@
+# -*- 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 = [
+    # Amazon kernel, machine, and ramdisk images
+    'TYPE_AKI',
+    'TYPE_AMI',
+    'TYPE_ARI',
+
+    # Optical media
+    'TYPE_ISO',
+
+    # Native format for QEMU
+    'TYPE_QCOW2',
+
+    # Unstructured generic byte-for-byte disk image
+    'TYPE_RAW',
+
+    # Native format for VirtualBox
+    'TYPE_VDI',
+
+    # VHD, VHDX disk (VMware, Xen, Microsoft, VirtualBox, etc)
+    'TYPE_VHD',
+    'TYPE_VHDX',
+
+    # Native format for VMware
+    'TYPE_VMDK',
+]