问题描述：
写jmx文件后，文件首行无<?xml version='1.0' encoding='UTF-8'?>
原因分析：
查阅xml.etree.ElementTree API`文档
write(file, encoding="us-ascii", xml_declaration=None, default_namespace=None, method="xml", *, short_empty_elements=True)
项目中实际调用为tree.write(jmxPath,encoding='UTF-8')，即默认xml_declaration=None，写jmx文件时不写入xml声明
解决办法：
将tree.write(jmxPath,encoding='UTF-8') 改成
tree.write(jmxPath,encoding='UTF-8',xml_declaration=True)
