Add viewer autobuild.xml roundtrip test

Fix a missing EOL after </llsd> and add a roundtrip test of viewer autobuild xml.

Author: bennettgoble

llsd/serde_xml.py

@@ -163,7 +163,7 @@ def _write(self, something):
         self.stream.writelines([b'<?xml version="1.0" ?>', self._eol,
                                 b'<llsd>', self._eol])
         self._generate(something)
-        self.stream.write(b'</llsd>')
+        self.stream.write(b'</llsd>' + self._eol)
 
 
 class LLSDXMLPrettyFormatter(LLSDXMLFormatter):