Fix sinfo route HTTP verb and headers

Recently, all main API routes use GET instead of POST and the
authentication token use the Authorization HTTP header. Use the same
things for the route /sinfo API route.

rest/slurmrestapi.py

@@ -420,9 +420,9 @@ def convert_nodeset():
     return json.dumps(list(NodeSet(data['nodeset'].encode('ascii', 'ignore'))))
 
 
-@app.route('/sinfo', methods=['POST', 'OPTIONS'])
-@crossdomain(origin=origins, methods=['POST'],
-             headers=['Accept', 'Content-Type', 'X-Requested-With'])
+@app.route('/sinfo', methods=['GET', 'OPTIONS'])
+@crossdomain(origin=origins, methods=['GET'],
+             headers=['Accept', 'Content-Type', 'X-Requested-With', 'Authorization'])
 @authentication_verify()
 def sinfo():