title: CDATA getting stripped in lxml even after using strip_cdata=False
body: <p>I have a requirement in which I need to read a XML file and replace a string with a certain value. The XML contains CDATA element and I need to preserve it. 
  I have tried using parser and setting strip_data to false. This is not working and need help to figure out a way to achieve it.</p>
  
  <pre><code>import lxml.etree as ET
  
  parser1 = ET.XMLParser(strip_cdata=False)
  
  with open('testxml.xml', encoding="utf8") as f:
  tree = ET.parse(f, parser=parser1)
  
  root = tree.getroot()
  for elem in root.getiterator():
      try:
          elem.text = elem.text.replace('Bundled Manager 2.2(8b)', '123456')
      except AttributeError:
          pass
  
  tree.write('output_new8.xml', xml_declaration=True, method='xml',  encoding="utf8")
  </code></pre>
  
  <p>Below is the Sample xml:</p>
  
  <hr>
  
  <pre><code>     &lt;?xml version="1.0" encoding="UTF-8" standalone="no"?&gt;&lt;!-- Copyright   (c) 2015 Moto Company, LLC. All rights reserved. Moto Confidential/Proprietary Information --&gt;
  &lt;Benchmark&gt;
         &lt;status date="2013-03-11"&gt;draft&lt;/status&gt;
      &lt;title&gt;Logitech TMM block(TM) System 300 Release Certification Matrix&lt;/title&gt;
      &lt;description&gt;Random discription&lt;/description&gt;
      &lt;version time="2013-03-05T15:20:20.995-04:00" update=""&gt;3.0.0-2017.03.00&lt;/version&gt;
          &lt;model system="urn:xccdf:scoring:default"/&gt;
      &lt;Profile id="xccdf_com.Moto_profile_release_4.0.21"&gt;
          &lt;status date="2016-03-30"&gt;draft&lt;/status&gt;
          &lt;title&gt;RCM 4.0.21&lt;/title&gt;
          &lt;description&gt;&lt;![CDATA[&lt;p&gt;Moto Vblock System 300 Release 4.0.21&lt;/p&gt;
  &lt;ul&gt;&lt;li&gt; TMM VNX OE for File was updated to 7.1.79.8.&lt;/li&gt;
  &lt;/ul&gt;]]&gt;
  &lt;/description&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vision_content_version"&gt;3.0.0-2015.07.00&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vision_version"&gt;3.0.0&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vplex_version"&gt;5.3.0.03.00.04&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_powerpath_version"&gt;Bundled Manager 2.2(8b)&lt;/set-value&gt;       
          &lt;select idref="xccdf_com.Moto_rule_vnx_version" selected="true"/&gt;
          &lt;select idref="xccdf_com.Moto_rule_vplex_version" selected="true"/&gt;
      &lt;/Profile&gt;
  &lt;/Benchmark&gt;
  </code></pre>
  
  <p>The output of the code is shown below:</p>
  
  <pre><code>&lt;?xml version='1.0' encoding='UTF8'?&gt;
  &lt;!-- Copyright (c) 2015 Moto Company, LLC. All rights reserved. Moto Confidential/Proprietary Information --&gt;&lt;Benchmark&gt;
      &lt;status date="2013-03-11"&gt;draft&lt;/status&gt;
      &lt;title&gt;Logitech TMM block(TM) System 300 Release Certification Matrix&lt;/title&gt;
      &lt;description&gt;Random discription&lt;/description&gt;
      &lt;version time="2013-03-05T15:20:20.995-04:00" update=""&gt;3.0.0-2017.03.00&lt;/version&gt;
          &lt;model system="urn:xccdf:scoring:default"/&gt;
      &lt;Profile id="xccdf_com.Moto_profile_release_4.0.21"&gt;
          &lt;status date="2016-03-30"&gt;draft&lt;/status&gt;
          &lt;title&gt;RCM 4.0.21&lt;/title&gt;
          &lt;description&gt;&amp;lt;p&amp;gt;Moto Vblock System 300 Release 4.0.21&amp;lt;/p&amp;gt;
  &amp;lt;ul&amp;gt;&amp;lt;li&amp;gt; TMM VNX OE for File was updated to 7.1.79.8.&amp;lt;/li&amp;gt;
  &amp;lt;/ul&amp;gt;
  &lt;/description&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vision_content_version"&gt;3.0.0-2015.07.00&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vision_version"&gt;3.0.0&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_vplex_version"&gt;5.3.0.03.00.04&lt;/set-value&gt;
          &lt;set-value idref="xccdf_com.Moto_value_powerpath_version"&gt;123456&lt;/set-value&gt;        
          &lt;select idref="xccdf_com.Moto_rule_vnx_version" selected="true"/&gt;
          &lt;select idref="xccdf_com.Moto_rule_vplex_version" selected="true"/&gt;
      &lt;/Profile&gt;
  &lt;/Benchmark
  </code></pre>
  
  <p>></p>
  
  <p>As you can see , CDATA section is stripped. 
  It will be great if someone can help me here.</p>