Cast 'instance-guid' to str, in order to avoid escaped syntax (!py!)

In the case of hellorina SR, the following section generated invalid command:

[proxy]
command-line = {{ python_location }}/bin/python2.7 {{ rina_proxy }} ${server:instance-guid} ${:ipv6} ${:port}
...

slapos/recipe/request.py

@@ -160,9 +160,10 @@ class Recipe(object):
       # Note: SlapOS Master does not support it for slave instances
       if not slave:
         try:
-          options['instance-guid'] = self.instance.getInstanceGuid()
+          options['instance-guid'] = self.instance.getInstanceGuid() \
+              .encode('UTF-8')
           # XXX: deprecated, to be removed
-          options['instance_guid'] = self.instance.getInstanceGuid()
+          options['instance_guid'] = options['instance-guid']
           options['instance-state'] = self.instance.getState()
           options['instance-status'] = self.instance.getStatus()
         except (slapmodule.ResourceNotReady, AttributeError):

slapos/recipe/slapconfiguration.py

@@ -155,7 +155,8 @@ class Recipe(object):
                                             'UNKNOWN Instance').encode('UTF-8')
       options['root-instance-title'] = parameter_dict.pop('root_instance_title',
                                             'UNKNOWN').encode('UTF-8')
-      options['instance-guid'] = computer_partition.getInstanceGuid()
+      options['instance-guid'] = computer_partition.getInstanceGuid() \
+          .encode('UTF-8')
 
       ipv4_set = set()
       v4_add = ipv4_set.add