pyocf: test update to handle zeroed metadata in attach

With atomic superblock commit during cache attach, it is possible
that power failure interrupts attach operation at a point where
neither new or old superblock is present - right after the superblock
is cleared.

Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>

tests/functional/tests/surprise_shutdown/test_management_surprise_shutdown.py

@@ -427,10 +427,19 @@ def test_surprise_shutdown_cache_reinit(pyocf_ctx):
 
         device.disarm()
 
+        cache = None
+        status = OcfErrorCode.OCF_OK
+        try:
             cache = Cache.load_from_device(device)
+        except OcfError as ex:
+            status = ex.error_code
 
+        if not cache:
+            assert status == OcfErrorCode.OCF_ERR_NO_METADATA
+        else:
             stats = cache.get_stats()
             if stats["conf"]["core_count"] == 0:
+                assert stats["usage"]["occupancy"]["value"] == 0
                 cache.add_core(core)
                 assert ocf_read(cache, core, io_offset) == Volume.VOLUME_POISON