Add get_highest_version method

Add method to query a server that supports /v3 endpoint and get the
highest supported microversion.

Change-Id: If179760787526440c852803eafaf9617bcd2d36e

cinderclient/api_versions.py

@@ -244,6 +244,18 @@ def _get_server_version_range(client):
             return APIVersion(version.min_version), APIVersion(version.version)
 
 
+def get_highest_version(client):
+    """Queries the server version info and returns highest supported
+    microversion
+
+    :param client: client object
+    :returns: APIVersion
+    """
+    server_start_version, server_end_version = _get_server_version_range(
+        client)
+    return server_end_version
+
+
 def discover_version(client, requested_version):
     """Checks ``requested_version`` and returns the most recent version
     supported by both the API and the client.

cinderclient/tests/unit/test_api_versions.py

@@ -253,3 +253,9 @@ class DiscoverVersionTestCase(utils.TestCase):
                              discovered_version.get_string())
             self.assertTrue(
                 self.fake_client.services.server_api_version.called)
+
+    def test_get_highest_version(self):
+        self._mock_returned_server_version("3.14", "3.0")
+        highest_version = api_versions.get_highest_version(self.fake_client)
+        self.assertEqual("3.14", highest_version.get_string())
+        self.assertTrue(self.fake_client.services.server_api_version.called)