Use Logger's built-in formatting

Passing concatenated strings into a logging method can incur a needless
performance hit because the concatenation will be performed every time
the method is called, whether or not the log level is low enough to show
the message.

Use built-in string formatting instead.

Change-Id: I0f5f0abfd13e0354ea5bb0f720b453e538ec4635
diff --git a/src/main/java/com/googlesource/gerrit/plugins/its/jira/JiraClient.java b/src/main/java/com/googlesource/gerrit/plugins/its/jira/JiraClient.java
index d02c816..ab1ca48 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/its/jira/JiraClient.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/its/jira/JiraClient.java
@@ -65,10 +65,10 @@
       case HTTP_OK:
         return true;
       case HTTP_NOT_FOUND:
-        log.error("Issue " + issueKey + " not found ");
+        log.error("Issue {} not found", issueKey);
         return false;
       case HTTP_FORBIDDEN:
-        log.error("No permission to read Issue " + issueKey);
+        log.error("No permission to read Issue {}", issueKey);
         return false;
       default:
         // Cannot happen due to passCodes filter