Raise if parsing, rendering, or writing fails

If jinja template parsing, rendering, or writing fails, we used to log
an error message and continue.  With this change, we'll raise the
original exception so we print the traceback and fail the build right
away.

Change-Id: I9e92d3aed844d965a425c43c79a8844e5c4bd006

tools/www-generator.py

@@ -65,7 +65,7 @@ def main():
         environment = jinja2.Environment(loader=loader)
     except Exception as e:
         logger.error("initialising template environment failed: %s" % e)
-        return 1
+        raise
 
     for templateFile in environment.list_templates():
         if not templateFile.endswith('.html'):
@@ -78,7 +78,7 @@ def main():
         except Exception as e:
             logger.error("parsing template %s failed: %s" %
                          (templateFile, e))
-            continue
+            raise
 
         try:
             output = lxml.html.tostring(
@@ -87,7 +87,7 @@ def main():
         except Exception as e:
             logger.error("rendering template %s failed: %s" %
                          (templateFile, e))
-            continue
+            raise
 
         try:
             target_directory = os.path.join(args.output_directory,
@@ -102,7 +102,7 @@ def main():
                 fh.write(output.encode('utf8'))
         except (IOError, OSError, UnicodeEncodeError) as e:
             logger.error("writing %s failed: %s" % (target_file, e))
-            continue
+            raise
 
     return 0