Cleanup inconsistent use of logging strings

[t92549]

In many places in Gaffer, correct logging string formatting is used:

Gaffer/store-implementation/accumulo-store/src/main/java/uk/gov/gchq/gaffer/accumulostore/operation/hdfs/handler/AddElementsFromHdfsHandler.java

Line 254 in fb63fc2

LOGGER.info("Ensuring output directory {} doesn't exist", outputPath);

However, in some places, string concatenation is incorrectly used instead:

Gaffer/store-implementation/accumulo-store/src/main/java/uk/gov/gchq/gaffer/accumulostore/operation/hdfs/handler/AddElementsFromHdfsHandler.java

Line 66 in fb63fc2

LOGGER.info("Using working directory for splits files: " + splitsFilePath);

Although concatenation works, it is considered bad practice as the concatenated string object is always created, whether or not that string will be logged (based on the logging level). However, with the former method of formatting, the object is only created if that string will be logged. This means better performance.
As well as that I find the formatting easier to read.

[RobertG111]

Hi. I have made a pull request regarding this issue #2651. Thanks.