Fix random_mac_generator to make proper EUI64s

The initial implementation of random_mac_generator created MAC addresses
that were one octet too long - the MAC addresses would have seven octets
instead of the proper EUI64-standard six.

This resolved testing issues in the consuming patch in Neutron (see
the change referenced in the Needed-By line).  A test is added that
replicates the conditions of the failure.  In the failed tests, the base
mac '12:34:56:78' was instead parsed so it became '12:34:56:7:8'; when
the code went to add 2 octets to the result, there were too many octets
to form a valid EUI64 MAC address.

Implements: blueprint speed-up-neutron-bulk-creation
Needed-By: https://review.openstack.org/584061
Change-Id: I9a2c40709db9204c7686500deac9ee8e8471b1bc

neutron_lib/tests/unit/utils/test_net.py

@@ -77,6 +77,14 @@ class TestRandomMacGenerator(base.BaseTestCase):
         self.assertEqual(['aa:bb:00:a2:a2:a2'], list(generator))
         mock_rnd.assert_called_with(8)
 
+    @mock.patch.object(random, 'getrandbits', return_value=0xa2)
+    def test_short_supplied_mac(self, mock_rnd):
+        mac_base = '12:34:56:78'
+        mac = mac_base.split(':')
+        generator = itertools.islice(net.random_mac_generator(mac), 1)
+        self.assertEqual(['12:34:56:78:a2:a2'], list(generator))
+        mock_rnd.assert_called_with(8)
+
 
 class TestPortDeviceOwner(base.BaseTestCase):
 

neutron_lib/utils/net.py

@@ -56,7 +56,7 @@ def random_mac_generator(base_mac):
     fixed = list(base_mac[0:3])
     to_generate = 3
     if base_mac[3] != '00':
-        fixed += base_mac[3]
+        fixed = list(base_mac[0:4])
         to_generate = 2
     beginning = ':'.join(fixed) + ':'