[SCB-752] provide a configuration to determine whether to output merged.log4j.properties

[yhs0092]

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See details in SCB-752

[coveralls]

Coverage increased (+0.02%) to 87.081% when pulling 2592afc on yhs0092:user_can_switch_off_merged_log4j_properties_file into 6c4c1c1 on apache:master.