Fix beautifulsoup warning

With current beautifulsoup package we get this warning when running
www-generator.py

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UserWarning: No parser was explicitly specified, so I'm using the best
available HTML parser for this system ("lxml"). This usually isn't a
problem, but if you run this code on another system, or in a different
virtual environment, it may use a different parser and behave
differently.

To get rid of this warning, change this:

 BeautifulSoup([your markup])

to this:

 BeautifulSoup([your markup], "lxml")
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Follow the advise to fix the warning.

Change-Id: I9409bac23797168296fee93f5398e6f5a9852a73

tools/www-generator.py

@@ -81,7 +81,7 @@ def main():
 
         try:
             output = template.render()
-            soup = BeautifulSoup(output)
+            soup = BeautifulSoup(output, "lxml")
             output = soup.prettify()
         except Exception as e:
             logger.error("rendering template %s failed: %s" %