DATAES-361 - Move Log4j2 config file to test sources.

The configuration file for Log4j2 had been added to src/main/resources accidentally which caused it to be picked up by user applications, e.g. in a Spring Boot application effectively disabling Boot's auto-configuration. This file has now been moved to the test resources.

Original pull request: spring-projects#191.
Related tickets: spring-projects/spring-boot#10634

Author: tsachev