Remove references to _i18n and apiclient.exceptions

Since oslo-incubator is no longer maintained[1] after
90ae25e38915cc502d9e9c52d59e8fb668a72ae1. We should cleanup
the deprecated code.

This patch do the following cleanup actions:
1. Use magnumclient.i18n instead of
magnumclient.openstack.common._i18n.
2. Use magnumclient.exceptions instead of the deprecated
magnumclient.openstack.common.apiclient.exceptions[2].

[1] http://lists.openstack.org/pipermail/openstack-dev/2015-November/
    079343.html
[2] https://github.com/openstack/python-magnumclient/blob/master/
    magnumclient/openstack/common/apiclient/exceptions.py#L25

Change-Id: I6fae1f84d211d661bb363e43167cdf8b6b06fd4d
Partial-Bug: #1529316

magnumclient/common/utils.py

@@ -17,8 +17,8 @@
 
 import json
 
-from magnumclient.openstack.common._i18n import _
-from magnumclient.openstack.common.apiclient import exceptions as exc
+from magnumclient import exceptions as exc
+from magnumclient.i18n import _
 
 
 def common_filters(marker=None, limit=None, sort_key=None, sort_dir=None):

magnumclient/shell.py

@@ -49,8 +49,8 @@ try:
 except ImportError:
     pass
 
+from magnumclient import exceptions as exc
 from magnumclient.openstack.common.apiclient import auth
-from magnumclient.openstack.common.apiclient import exceptions as exc
 from magnumclient.openstack.common import cliutils
 from magnumclient.v1 import client as client_v1
 from magnumclient.v1 import shell as shell_v1

magnumclient/tests/test_utils.py

@@ -18,7 +18,7 @@
 import six
 
 from magnumclient.common import utils
-from magnumclient.openstack.common.apiclient import exceptions as exc
+from magnumclient import exceptions as exc
 from magnumclient.openstack.common import cliutils
 from magnumclient.tests import utils as test_utils