Fix possible race condition applying schemas

Found an instance where two of these fired too close together, and
caused a fatal error. Use a write lock, and then catch the schema.apply
function in case it fails anyways.

node-daemon/pvcnoded/Daemon.py

@@ -197,7 +197,9 @@ def entrypoint():
         os.execv(sys.argv[0], sys.argv)
 
     # Validate the schema
-    pvcnoded.util.zookeeper.validate_schema(logger, zkhandler)
+    with zkhandler.writelock("base.schema.version"):
+        sleep(0.5)
+        pvcnoded.util.zookeeper.validate_schema(logger, zkhandler)
 
     # Define a cleanup function
     def cleanup(failure=False):

node-daemon/pvcnoded/util/zookeeper.py

@@ -94,7 +94,10 @@ def validate_schema(logger, zkhandler):
     # Validate our schema against the active version
     if not zkhandler.schema.validate(zkhandler, logger):
         logger.out("Found schema violations, applying", state="i")
-        zkhandler.schema.apply(zkhandler)
+        try:
+            zkhandler.schema.apply(zkhandler)
+        except Exception as e:
+            logger.out(f"Failed to apply schema updates: {e}", state="w")
     else:
         logger.out("Schema successfully validated", state="o")