Fix flavor create help re swap size units

nova actually expects and uses swap size in MB, while in openstackclient
currently help states that swap must be specified in GB and passes this
value to nova without changes.

Fix the help string.

Change-Id: I95f46246c072961ce77f818d80d75e6a51f728d0
Closes-Bug: #1656018

Author: pshchelo

doc/source/command-objects/flavor.rst

@@ -42,9 +42,9 @@ Create new flavor
 
     Ephemeral disk size in GB (default 0G)
 
-.. option:: --swap <size-gb>
+.. option:: --swap <size-mb>
 
-    Swap space size in GB (default 0G)
+    Swap space size in MB (default 0M)
 
 .. option:: --vcpus <num-cpu>
 

openstackclient/compute/v2/flavor.py

@@ -89,9 +89,9 @@ def get_parser(self, prog_name):
         parser.add_argument(
             "--swap",
             type=int,
-            metavar="<size-gb>",
+            metavar="<size-mb>",
             default=0,
-            help=_("Swap space size in GB (default 0G)")
+            help=_("Swap space size in MB (default 0M)")
         )
         parser.add_argument(
             "--vcpus",