Fix schema for all_tenants query parameter

... to resolve the following error in list snapshot API with the flag.

```
Invalid input for field/attribute all_tenants. Value: ['1']. ['1'] is
not of type 'boolean', 'string'
```

Change-Id: Id8c83b87b0000c25ae4bcebdbe97d5e096def33c
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

manila/api/schemas/share_snapshots.py

@@ -48,13 +48,13 @@ index_request_query = {
             'maxLength': 255,
         }),
         # Admin only
-        'all_tenants': {
+        'all_tenants': parameter_types.single_param({
             **parameter_types.boolean,
-            'enum': [1, 0],
             'description': (
                 "Set 1 to list resources for all projects;"
                 "set 0 to list resources only for the current project"
-            )},
+            )
+        }),
 
         # Basic filters
         'name': parameter_types.single_param({