Fix path handling for zkhandler

Using full paths broke the local schema generator, so convert these to
proper class instance methods and use them along with a new default +
settable override.

api-daemon/pvcapid-manage-zk.py

@@ -21,4 +21,5 @@
 
 from daemon_lib.zkhandler import ZKSchema
 
-ZKSchema.write()
+schema = ZKSchema(root_path=".")
+schema.write()