test-api: add string representation of SeqCutOffPolicy

Signed-off-by: Kamil Gierszewski <kamil.gierszewski@huawei.com>

test/functional/api/cas/cache_config.py

@@ -72,9 +72,9 @@ class CacheMode(Enum):
 
 
 class SeqCutOffPolicy(Enum):
-    full = 0
-    always = 1
-    never = 2
+    full = "full"
+    always = "always"
+    never = "never"
     DEFAULT = full
 
     @classmethod
@@ -85,6 +85,9 @@ class SeqCutOffPolicy(Enum):
 
         raise ValueError(f"{name} is not a valid sequential cut off name")
 
+    def __str__(self):
+        return self.value
+
 
 class MetadataMode(Enum):
     normal = "normal"