Add third element to RPC versions for backports

This makes the RPC version support three elements, adding a "revision"
in addition to the major and minor version. The revision would always
be zero for the master branch of a service, but could be incremented
for stable versions. This provides us some room to backport fixes
that affect RPC versions in such a way that would avoid breaking
the version lineage for systems running stable versions that may
some day be involved in a rolling upgrade to a version from master.

I didn't find any tests for version_is_compatible(), so I added
some for existing version scenarios, as well as new ones with
revisions. They also serve to validate that this doesn't break
anything for code using two-element versions (the expectation is that
two-element versions will still be used everywhere until a third
is needed).

Porting chages from Change-Id I239c17a3e305f572493498c4b96ee3c7514c5881
to oslo-incubator

Change-Id: I4fa7b0be14a7afba36136a746b76036355f119b2

oslo/messaging/_utils.py

@@ -22,8 +22,20 @@ def version_is_compatible(imp_version, version):
     """
     version_parts = version.split('.')
     imp_version_parts = imp_version.split('.')
+    try:
+        rev = version_parts[2]
+    except IndexError:
+        rev = 0
+    try:
+        imp_rev = imp_version_parts[2]
+    except IndexError:
+        imp_rev = 0
+
     if int(version_parts[0]) != int(imp_version_parts[0]):  # Major
         return False
     if int(version_parts[1]) > int(imp_version_parts[1]):  # Minor
         return False
+    if (int(version_parts[1]) == int(imp_version_parts[1]) and
+            int(rev) > int(imp_rev)):  # Revision
+        return False
     return True

tests/test_utils.py

@@ -0,0 +1,49 @@
+
+# Copyright 2013 Red Hat, Inc.
+#
+#    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.
+
+from oslo.messaging import _utils as utils
+from tests import utils as test_utils
+
+
+class PoolTestCase(test_utils.BaseTestCase):
+    def test_version_is_compatible_same(self):
+        self.assertTrue(utils.version_is_compatible('1.23', '1.23'))
+
+    def test_version_is_compatible_newer_minor(self):
+        self.assertTrue(utils.version_is_compatible('1.24', '1.23'))
+
+    def test_version_is_compatible_older_minor(self):
+        self.assertFalse(utils.version_is_compatible('1.22', '1.23'))
+
+    def test_version_is_compatible_major_difference1(self):
+        self.assertFalse(utils.version_is_compatible('2.23', '1.23'))
+
+    def test_version_is_compatible_major_difference2(self):
+        self.assertFalse(utils.version_is_compatible('1.23', '2.23'))
+
+    def test_version_is_compatible_newer_rev(self):
+        self.assertFalse(utils.version_is_compatible('1.23', '1.23.1'))
+
+    def test_version_is_compatible_newer_rev_both(self):
+        self.assertFalse(utils.version_is_compatible('1.23.1', '1.23.2'))
+
+    def test_version_is_compatible_older_rev_both(self):
+        self.assertTrue(utils.version_is_compatible('1.23.2', '1.23.1'))
+
+    def test_version_is_compatible_older_rev(self):
+        self.assertTrue(utils.version_is_compatible('1.24', '1.23.1'))
+
+    def test_version_is_compatible_no_rev_is_zero(self):
+        self.assertTrue(utils.version_is_compatible('1.23.0', '1.23'))