[SPARK-26650][CORE] Demote noisy HBase-related log message.

Make it a debug message so that it doesn't show up in the vast
majority of cases, where HBase classes are not available.

Closes #23776 from vanzin/SPARK-26650.

Authored-by: Marcelo Vanzin <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: Marcelo Vanzin

core/src/main/scala/org/apache/spark/deploy/security/HBaseDelegationTokenProvider.scala

@@ -120,7 +120,9 @@ private[security] class HBaseDelegationTokenProvider
       confCreate.invoke(null, conf).asInstanceOf[Configuration]
     } catch {
       case NonFatal(e) =>
-        logWarning("Fail to invoke HBaseConfiguration", e)
+        // Keep at debug level since this is executed even when HBase tokens are not needed.
+        // Avoids a noisy warning for users who don't care about HBase.
+        logDebug("Unable to load HBaseConfiguration.", e)
         conf
     }
   }