Prepare backward compatibility.

Allow to have not defined buildout binary.

slapos/grid/slapgrid.py

@@ -87,7 +87,8 @@ def parseArgumentTupleAndReturnSlapgridObject(*argument_tuple):
   parser.add_argument("--usage-report-periodicity",
                     type=int, default="24",
                     help="The periodicity of usage report sends, in hours.")
-  parser.add_argument("--buildout", help="Location of buildout binary.")
+  parser.add_argument("--buildout", help="Location of buildout binary.",
+                    default=None)
   parser.add_argument("--pidfile",
                     help="The location where pidfile will be created.")
   parser.add_argument("--logfile",
@@ -197,7 +198,7 @@ def parseArgumentTupleAndReturnSlapgridObject(*argument_tuple):
             master_ca_file=master_ca_file,
             certificate_repository_path=certificate_repository_path,
             console=option_dict['console'],
-            buildout=option_dict['buildout']),
+            buildout=option_dict.get('buildout')),
           option_dict])