[#91] Failover enhancements

Signed-off-by: Andrey Berezin <a.berezin@yadro.com>

src/frostfs_testlib/healthcheck/interfaces.py

@@ -0,0 +1,9 @@
+from abc import ABC, abstractmethod
+
+from frostfs_testlib.storage.cluster import ClusterNode
+
+
+class Healthcheck(ABC):
+    @abstractmethod
+    def perform(self, cluster_node: ClusterNode):
+        """Perform healthcheck on the target cluster node"""