HV-1859 Upgrade to Log4j 2 2.15.0

This is only a test dependency so we are not affected by the CVE but
let's fix it anyway.

Author: gsmet

pom.xml

@@ -136,7 +136,7 @@
         <version.com.fasterxml.classmate>1.5.1</version.com.fasterxml.classmate>
         <version.joda-time>2.9.7</version.joda-time>
         <version.org.slf4j>1.7.22</version.org.slf4j>
-        <version.org.apache.logging.log4j>2.13.3</version.org.apache.logging.log4j>
+        <version.org.apache.logging.log4j>2.15.0</version.org.apache.logging.log4j>
 
         <!--
             These dependencies are used for integration tests with WildFly.