Fixed subnet command host route output

Fixed the "os subnet create", "os subnet list" and
"os subnet show" command output for host routes to
improve readability and to align with the "--host-route"
option on the "os subnet create" and "os subnet set"
commands.

Change-Id: Ida69ae1a0bdb2e1648f8b5c978fc80cf1bbe752f
Closes-Bug: #1572309

openstackclient/network/v2/subnet.py

@@ -14,8 +14,6 @@
 """Subnet action implementations"""
 import copy
 
-from json.encoder import JSONEncoder
-
 from openstackclient.common import command
 from openstackclient.common import exceptions
 from openstackclient.common import parseractions
@@ -31,10 +29,8 @@ def _format_allocation_pools(data):
 
 
 def _format_host_routes(data):
-    try:
+    # Map the host route keys to match --host-route option.
-        return '\n'.join([JSONEncoder().encode(route) for route in data])
+    return utils.format_list_of_dicts(convert_entries_to_gateway(data))
-    except (TypeError, KeyError):
-        return ''
 
 
 _formatters = {
@@ -89,8 +85,9 @@ def convert_entries_to_nexthop(entries):
     # Change 'gateway' entry to 'nexthop'
     changed_entries = copy.deepcopy(entries)
     for entry in changed_entries:
-        entry['nexthop'] = entry['gateway']
+        if 'gateway' in entry:
-        del entry['gateway']
+            entry['nexthop'] = entry['gateway']
+            del entry['gateway']
 
     return changed_entries
 
@@ -99,8 +96,9 @@ def convert_entries_to_gateway(entries):
     # Change 'nexthop' entry to 'gateway'
     changed_entries = copy.deepcopy(entries)
     for entry in changed_entries:
-        entry['gateway'] = entry['nexthop']
+        if 'nexthop' in entry:
-        del entry['nexthop']
+            entry['gateway'] = entry['nexthop']
+            del entry['nexthop']
 
     return changed_entries