Make the OS object able to represent broken OSes

Till now the OS object just represents a correct OS instance.  Change it so it
can represent a broken one too, by adding a "status" field: if this field is
different from the OS_VALID_STATUS constant the object is considered to be an
invalid OS, the "status" field to be a debugging message, and its boolean
status is set to false.

Reviewed-By: iustinp

lib/constants.py

@@ -130,6 +130,9 @@ LOCALHOST_IP_ADDRESS = "127.0.0.1"
 TCP_PING_TIMEOUT = 10
 GANETI_RUNAS = "root"
 
+# valid os status
+OS_VALID_STATUS = "VALID"
+
 # ssh constants
 SSH_INITD_SCRIPT = _autoconf.SSH_INITD_SCRIPT
 SSH_CONFIG_DIR = "/etc/ssh/"

lib/objects.py

@@ -589,6 +589,7 @@ class OS(ConfigObject):
   __slots__ = [
     "name",
     "path",
+    "status",
     "api_version",
     "create_script",
     "export_script",
@@ -596,6 +597,10 @@ class OS(ConfigObject):
     "rename_script",
     ]
 
+  def __nonzero__(self):
+    return self.status == constants.OS_VALID_STATUS
+
+  __bool__ = __nonzero__
 
 class Node(TaggableObject):
   """Config object representing a node."""