nova-status: don't coerce version numbers to floats for comparison

As is comparison will fail when Placement API version 1.10 is
released, e.g. in the case: float('1.10') < float('1.4').

Use the helper provided by pkg_resources instead. The returned
values can be compared and sorted and have a string representation.

http://setuptools.readthedocs.io/en/latest/pkg_resources.html#parsing-utilities

Change-Id: Iaaca8f458671bd518b4c10c776f78b9c1ed803dd

nova/cmd/status.py

@@ -28,6 +28,7 @@ import traceback
 from keystoneauth1 import exceptions as ks_exc
 from keystoneauth1 import loading as keystone
 from oslo_config import cfg
+import pkg_resources
 import prettytable
 from sqlalchemy import func as sqlfunc
 from sqlalchemy import MetaData, Table, select
@@ -200,10 +201,11 @@ class UpgradeCommands(object):
         """
         try:
             versions = self._placement_get("/")
-            max_version = float(versions["versions"][0]["max_version"])
+            max_version = pkg_resources.parse_version(
+                versions["versions"][0]["max_version"])
             # NOTE(rpodolyaka): 1.4 is needed in Pike and further as
             # FilterScheduler will no longer fall back to not using placement
-            needs_version = 1.4
+            needs_version = pkg_resources.parse_version("1.4")
             if max_version < needs_version:
                 msg = (_('Placement API version %(needed)s needed, '
                          'you have %(current)s.') %

nova/tests/unit/cmd/test_status.py

@@ -218,6 +218,26 @@ class TestPlacementCheck(test.NoDBTestCase):
         res = self.cmd._check_placement()
         self.assertEqual(status.UpgradeCheckCode.SUCCESS, res.code)
 
+    @mock.patch.object(status.UpgradeCommands, "_placement_get")
+    def test_version_comparison_does_not_use_floats(self, get):
+        # NOTE(rpodolyaka): previously _check_placement() coerced the version
+        # numbers to floats prior to comparison, that would lead to failures
+        # in cases like float('1.10') < float('1.4'). As we require 1.4+ now,
+        # the _check_placement() call below will assert that version comparison
+        # continues to work correctly when Placement API versions 1.10
+        # (or newer) is released
+        get.return_value = {
+             "versions": [
+                {
+                    "min_version": "1.0",
+                    "max_version": "1.10",
+                    "id": "v1.0"
+                }
+            ]
+        }
+        res = self.cmd._check_placement()
+        self.assertEqual(status.UpgradeCheckCode.SUCCESS, res.code)
+
     @mock.patch.object(status.UpgradeCommands, "_placement_get")
     def test_invalid_version(self, get):
         get.return_value = {