views: improve checks for space available in cache

Use the new "free_cache" field in GET /cache/list to check
against the real available space to check if an image fits in
cache.

ogcp/views.py

@@ -956,20 +956,17 @@ def image_fits_in_cache(server, clients_info, image):
 
     for client_info in clients_info:
         ip = client_info['ip']
-        cache_size = int(client_info['cache_size'])
-        used_cache = 0
+        cache_size = client_info['cache_size'] * 1024
         has_image = False;
 
         for image_info in client_info['images']:
-            used_cache += int(image_info['size'])
-
             if image_info['checksum'] == image_checksum:
                 has_image = True
 
         if has_image:
             continue
 
-        free_cache = cache_size - used_cache
+        free_cache = client_info['free_cache']
         if free_cache < image_size:
             missing_cache = image_size - free_cache
             err_report += f'{ip} requires {(missing_cache / (1024 ** 3)):.3f} free GiB<br>'