Fix version negotiation

When the python client catch a 406 (Not Acceptable) error talking to
an older version of the Ironic server the client will try to negotiate
and fall back to the minimum supported version. Before the code was
determining the minimum version by using the builtin min() method with
strings but the result doesn't always come correct by doing it, e.g:

In [1]: min('1.10', '1.6')
Out[1]: '1.10'

In [2]: min('1.9', '1.6')
Out[2]: '1.6'

This patch fix this problem with the version negotiation.

Closes-Bug: #1475308
Change-Id: I2c756288d9590d1d18574a787601681b235fb57d

ironicclient/common/http.py

@@ -14,6 +14,7 @@
 #    under the License.
 
 import copy
+from distutils.version import StrictVersion
 import functools
 import json
 import logging
@@ -126,7 +127,8 @@ class VersionNegotiationMixin(object):
                 % {'req': self.os_ironic_api_version,
                    'min': min_ver, 'max': max_ver}))
 
-        negotiated_ver = min(self.os_ironic_api_version, max_ver)
+        negotiated_ver = str(min(StrictVersion(self.os_ironic_api_version),
+                                 StrictVersion(max_ver)))
         if negotiated_ver < min_ver:
             negotiated_ver = min_ver
         # server handles microversions, but doesn't support

ironicclient/tests/unit/test_http.py

@@ -116,7 +116,7 @@ class VersionNegotiationMixinTest(utils.BaseTestCase):
                        autospec=True)
     def test_negotiate_version_server_newer(self, mock_pvh, mock_save_data):
         # Test newer server and older client
-        mock_pvh.return_value = ('1.1', '99.99')
+        mock_pvh.return_value = ('1.1', '1.10')
         mock_conn = mock.MagicMock()
         result = self.test_object.negotiate_version(mock_conn, self.response)
         self.assertEqual('1.6', result)