python: fix check-python errors in plugins

Fixes some lint errors with unused variables:

contrib/plugins/fail/failtimeout.py:48:5:
  F841 local variable 'e' is assigned to but never used

contrib/plugins/helloworld.py:86:5:
  F841 local variable 'e' is assigned to but never used

Signed-off-by: William Casarin <jb55@jb55.com>

contrib/plugins/fail/failtimeout.py

@@ -45,7 +45,7 @@ for l in sys.stdin:
             "result": result,
             "id": request['id']
         }
-    except Exception as e:
+    except Exception:
         result = {
             "jsonrpc": "2.0",
             "error": "Error while processing {}".format(request['method']),

contrib/plugins/helloworld.py

@@ -83,7 +83,7 @@ for l in sys.stdin:
             "result": result,
             "id": request['id']
         }
-    except Exception as e:
+    except Exception:
         result = {
             "jsonrpc": "2.0",
             "error": "Error while processing {}".format(request['method']),