fix warnings from test suite

This branch fixes some test runner warnings such as:

Test delete non exists note after pull ... /usr/lib/python2.7/dist-packages/sqlalchemy/sql/expression.py:1927: SAWarning: The IN-predicate on "notes.id" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate.  Consider alternative strategies for improved performance.
  return self._in_impl(operators.in_op, operators.notin_op, other)
/usr/lib/python2.7/dist-packages/sqlalchemy/sql/expression.py:1927: SAWarning: The IN-predicate on "notes.conflict_parent_id" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate.  Consider alternative strategies for improved performance.
  return self._in_impl(operators.in_op, operators.notin_op, other)
ok
Test delete notebooks after pull ... /usr/lib/python2.7/dist-packages/sqlalchemy/sql/expression.py:1927: SAWarning: The IN-predicate on "notebooks.id" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate.  Consider alternative strategies for improved performance.
  return self._in_impl(operators.in_op, operators.notin_op, other)
ok
Test delete non exists after pull ... /usr/lib/python2.7/dist-packages/sqlalchemy/sql/expression.py:1927: SAWarning: The IN-predicate on "tags.id" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate.  Consider alternative strategies for improved performance.
  return self._in_impl(operators.in_op, operators.notin_op, other)
ok