flake8: fix local variable unused cases

Fix several cases of F841 local variable is assigned to but never used.

Part of #270

Author: DifferentialOrange

tarantool/connection_pool.py

@@ -569,7 +569,8 @@ def _get_new_state(self, unit):
         try:
             read_only = resp.data[0]['ro']
         except (IndexError, KeyError) as exc:
-            msg = f"Incorrect box.info response from {unit.addr['host']}:{unit.addr['port']}"
+            msg = (f"Incorrect box.info response from {unit.addr['host']}:{unit.addr['port']}"
+                   f"reason: {repr(exc)}")
             warn(msg, PoolTolopogyWarning)
             return InstanceState(Status.UNHEALTHY)
 
@@ -581,7 +582,8 @@ def _get_new_state(self, unit):
                 warn(msg, PoolTolopogyWarning)
                 return InstanceState(Status.UNHEALTHY)
         except (IndexError, KeyError) as exc:
-            msg = f"Incorrect box.info response from {unit.addr['host']}:{unit.addr['port']}"
+            msg = (f"Incorrect box.info response from {unit.addr['host']}:{unit.addr['port']}"
+                   f"reason: {repr(exc)}")
             warn(msg, PoolTolopogyWarning)
             return InstanceState(Status.UNHEALTHY)