Add tests for proper statistics display

Signed-off-by: Rafal Stefanowski <rafal.stefanowski@intel.com>

test/functional/api/cas/casadm_params.py

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: BSD-3-Clause-Clear
 #
 
-from enum import Enum
+from aenum import Enum
 
 
 class OutputFormat(Enum):
@@ -12,9 +12,12 @@ class OutputFormat(Enum):
 
 
 class StatsFilter(Enum):
-    all = 0
-    conf = 1
-    usage = 2
-    req = 3
-    blk = 4
-    err = 5
+    all = "all"
+    conf = "configuration"
+    usage = "usage"
+    req = "request"
+    blk = "block"
+    err = "error"
+
+    def __str__(self):
+        return self.value