Create message variables for exceptions

Instead of inline messages, let's create variables instead, as
it's easier to find strings, and mark them for translation.

Change-Id: Ibbcfdbc59d12a0cb4af50f73043d3ff7f3c76f99

openstackclient/compute/v2/keypair.py

@@ -57,8 +57,9 @@ class CreateKeypair(show.ShowOne):
                 with open(os.path.expanduser(parsed_args.public_key)) as p:
                     public_key = p.read()
             except IOError as e:
-                raise exceptions.CommandError(
-                    "Key file %s not found: %s" % (parsed_args.public_key, e))
+                msg = "Key file %s not found: %s"
+                raise exceptions.CommandError(msg
+                                              % (parsed_args.public_key, e))
 
         keypair = compute_client.keypairs.create(
             parsed_args.name,

openstackclient/compute/v2/server.py

@@ -300,19 +300,22 @@ class CreateServer(show.ShowOne):
                 raise exceptions.CommandError("Can't open '%s': %s" % (src, e))
 
         if parsed_args.min > parsed_args.max:
-            raise exceptions.CommandError("min instances should be <= "
-                                          "max instances")
+            msg = "min instances should be <= max instances"
+            raise exceptions.CommandError(msg)
         if parsed_args.min < 1:
-            raise exceptions.CommandError("min instances should be > 0")
+            msg = "min instances should be > 0"
+            raise exceptions.CommandError(msg)
         if parsed_args.max < 1:
-            raise exceptions.CommandError("max instances should be > 0")
+            msg = "max instances should be > 0"
+            raise exceptions.CommandError(msg)
 
         userdata = None
         if parsed_args.user_data:
             try:
                 userdata = open(parsed_args.user_data)
             except IOError as e:
-                raise exceptions.CommandError("Can't open '%s': %s" %
+                msg = "Can't open '%s': %s"
+                raise exceptions.CommandError(msg %
                                               (parsed_args.user_data, e))
 
         block_device_mapping = dict(v.split('=', 1)
@@ -1077,8 +1080,8 @@ class SetServer(command.Command):
             if p1 == p2:
                 server.change_password(p1)
             else:
-                raise exceptions.CommandError(
-                    "Passwords do not match, password unchanged")
+                msg = "Passwords do not match, password unchanged"
+                raise exceptions.CommandError(msg)
 
 
 class ShowServer(show.ShowOne):

openstackclient/network/v2/network.py

@@ -206,7 +206,8 @@ class SetNetwork(command.Command):
         if parsed_args.shared is not None:
             body['shared'] = parsed_args.shared
         if body == {}:
-            raise exceptions.CommandError("Nothing specified to be set")
+            msg = "Nothing specified to be set"
+            raise exceptions.CommandError(msg)
         update_method = getattr(client, "update_network")
         update_method(_id, {'network': body})
         return