Remove unnecessary output

[homper]

For example, this script

#!/usr/bin/env python3
# coding: utf-8

import testgres

node = testgres.get_new_node()
node.init()
node.start()
node.safe_psql("CREATE TABLE IF NOT EXISTS o_test (val int);")
node.execute("INSERT INTO o_test VALUES (1);")
print(node.execute("TABLE o_test;")[0][0])
node.execute("UPDATE o_test SET val = 2;")
print(node.execute("TABLE o_test;")[0][0])
node.stop()

prints

python t/checkpointer_test.py
Error executing query: attempting to use unexecuted cursor
1
Error executing query: attempting to use unexecuted cursor
2

This is probably not the intended behavior

[demonolock]

@homper Thank you! Will add it to the next release