fix: Clarify wording when Ray on Vertex cluster is missing head node ip

PiperOrigin-RevId: 585711565

Author: matthew29tang

google/cloud/aiplatform/preview/vertex_ray/client_builder.py

@@ -97,7 +97,7 @@ def __init__(self, address: Optional[str]) -> None:
             raise ValueError(
                 "[Ray on Vertex AI]: Ray Cluster ",
                 persistent_resource_id,
-                " failed to start Head node properly.",
+                " Head node is not reachable. Please ensure that a valid VPC network has been specified.",
             )
         # Handling service_account
         service_account = (
@@ -106,7 +106,7 @@ def __init__(self, address: Optional[str]) -> None:
 
         if service_account:
             raise ValueError(
-                "[Ray on Vertex AI]: Cluster ",
+                "[Ray on Vertex AI]: Ray Cluster ",
                 address,
                 " failed to start Head node properly because custom service account isn't supported.",
             )