[Misc] Small refactoring to use a method unstead of a class variable

xwiki-platform-core/xwiki-platform-test/xwiki-platform-test-docker/src/main/java/org/xwiki/test/docker/junit5/servletengine/ServletEngine.java

@@ -142,7 +142,7 @@ public String getHostIP()
      */
     public String getInternalIP()
     {
-        return isOutsideDocker ? HOST_INTERNAL : "xwikiweb";
+        return isOutsideDocker() ? HOST_INTERNAL : "xwikiweb";
     }
 
     /**
@@ -179,6 +179,6 @@ public String getPermanentDirectory()
      */
     public String getDockerImageName()
     {
-        return dockerImageName;
+        return this.dockerImageName;
     }
 }