Add a comment to this workitem

        :param msg: comment message
        :return: the :class:`rtcclient.models.Comment` object
        :rtype: rtcclient.models.Comment

def addComment(self, msg=None):
        """Add a comment to this workitem

        :param msg: comment message
        :return: the :class:`rtcclient.models.Comment` object
        :rtype: rtcclient.models.Comment
        """

        origin_comment = '''
<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:rtc_ext="http://jazz.net/xmlns/prod/jazz/rtc/ext/1.0/"
    xmlns:rtc_cm="http://jazz.net/xmlns/prod/jazz/rtc/cm/1.0/"
    xmlns:oslc_cm="http://open-services.net/ns/cm#"
    xmlns:dcterms="http://purl.org/dc/terms/"
    xmlns:oslc_cmx="http://open-services.net/ns/cm-x#"
    xmlns:oslc="http://open-services.net/ns/core#">
  <rdf:Description rdf:about="{0}">
    <rdf:type rdf:resource="http://open-services.net/ns/core#Comment"/>
    <dcterms:description rdf:parseType="Literal">{1}</dcterms:description>
  </rdf:Description>
</rdf:RDF>
'''

        comments_url = "/".join([self.url,
                                 "rtc_cm:comments"])
        headers = copy.deepcopy(self.rtc_obj.headers)
        resp = self.get(comments_url,
                        verify=False,
                        proxies=self.rtc_obj.proxies,
                        headers=headers)

        raw_data = xmltodict.parse(resp.content)

        total_cnt = raw_data["oslc_cm:Collection"]["@oslc_cm:totalCount"]
        comment_url = "/".join([comments_url,
                                total_cnt])

        comment_msg = origin_comment.format(comment_url, msg)

        headers["Content-Type"] = self.OSLC_CR_RDF
        headers["Accept"] = self.OSLC_CR_RDF
        headers["OSLC-Core-Version"] = "2.0"
        headers["If-Match"] = resp.headers.get("etag")
        req_url = "/".join([comments_url,
                            "oslc:comment"])

        resp = self.post(req_url,
                         verify=False,
                         headers=headers,
                         proxies=self.rtc_obj.proxies,
                         data=comment_msg)
        self.log.info("Successfully add comment: [%s] for <Workitem %s>",
                      msg, self)

        raw_data = xmltodict.parse(resp.content)
        return Comment(comment_url,
                       self.rtc_obj,
                       raw_data=raw_data["rdf:RDF"]["rdf:Description"])