RuleBase: Tidy up log messages

* Use log built-in formatter.
* Reformat lines to improve readability.

Change-Id: I7afee984427fffc58d357a554a7bf907163f6f4e
diff --git a/src/main/java/com/googlesource/gerrit/plugins/its/base/workflow/RuleBase.java b/src/main/java/com/googlesource/gerrit/plugins/its/base/workflow/RuleBase.java
index 41dc9fa..3a7b0c5 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/its/base/workflow/RuleBase.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/its/base/workflow/RuleBase.java
@@ -148,16 +148,12 @@
     if (!globalRuleFile.exists() && !itsSpecificRuleFile.exists()) {
       try {
         log.warn(
-            "Neither global rule file "
-                + globalRuleFile.getCanonicalPath()
-                + " nor Its specific rule file"
-                + itsSpecificRuleFile.getCanonicalPath()
-                + " exist. Please configure "
-                + "rules.");
+            "Neither global rule file {} nor Its specific rule file {} exist. Please configure rules.",
+            globalRuleFile.getCanonicalPath(),
+            itsSpecificRuleFile.getCanonicalPath());
       } catch (IOException e) {
         log.warn(
-            "Neither global rule file nor Its specific rule files exist. "
-                + "Please configure rules.");
+            "Neither global rule file nor Its specific rule files exist. Please configure rules.");
       }
     }
   }