RemoteOperations::exec_command does not handle 'expect_error' parameter correctly

[dmitry-lipetsk]

RemoteOperations::exec_command must not raise and Exception when we define expect_error = True

testgres/testgres/operations/remote_ops.py

Lines 90 to 91 in cf1d227

	if expect_error:
	raise Exception(result, error)

Test case:

    def test_exec_command_failure__expect_error(self):
        """
        Test exec_command for command execution failure.
        """
        cmd = "nonexistent_command"

        exit_status, result, error = self.operations.exec_command(cmd, verbose=True, wait_exit=True, shell=True, expect_error=True)

        assert error == b'bash: line 1: nonexistent_command: command not found\n'
        assert exit_status == 127
        assert result == b''