Improve logging in MongoChangeSetPersister [DATAMONGO-1380]

[spring-projects-issues]

Mark Paluch opened DATAMONGO-1380 and commented

Wrap debug level logging in isDebugEnabled() conditions, use slf4j-style for arguments in logging

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Referenced from: pull request #317

Backported to: 1.8.4 (Gosling SR4), 1.7.3 (Fowler SR3)