Internationalization (i18n) - Enable French locale

Our project should now enable its internationalization.
This patchset add the french locale to the project but also
refactors the codebase to following the oslo_i18n recommendations.

DocImpact
Implements: blueprint support-translation

Change-Id: I0e4fbf05d16afb5e25bac78438c640f147c754b1

watcher/api/controllers/v1/types.py

@@ -21,8 +21,8 @@ import six
 import wsme
 from wsme import types as wtypes
 
+from watcher._i18n import _
 from watcher.common import exception
-from watcher.common.i18n import _
 from watcher.common import utils
 
 

watcher/api/controllers/v1/utils.py

@@ -17,7 +17,7 @@ import jsonpatch
 from oslo_config import cfg
 import wsme
 
-from watcher.common.i18n import _
+from watcher._i18n import _
 
 CONF = cfg.CONF
 

watcher/api/middleware/auth_token.py

@@ -19,8 +19,8 @@ from oslo_log import log
 
 from keystonemiddleware import auth_token
 
+from watcher._i18n import _
 from watcher.common import exception
-from watcher.common.i18n import _
 from watcher.common import utils
 
 LOG = log.getLogger(__name__)

watcher/api/middleware/parsable_error.py

@@ -27,8 +27,8 @@ from oslo_log import log
 import six
 import webob
 
-from watcher.common.i18n import _
-from watcher.common.i18n import _LE
+from watcher._i18n import _
+from watcher._i18n import _LE
 
 LOG = log.getLogger(__name__)