Fix debug log in AlluxioJniFuseFileSystem

[dbw9580]

https://github.com/Alluxio/alluxio/blob/8dcbc1051c4bff18391afb33e198e778bd37bb9b/integration/fuse/src/main/java/alluxio/fuse/AlluxioJniFuseFileSystem.java#L415-L416

The debug log should use the internal formatting capability of Slf4J, so that when debug level logging is not enabled, a new string will not be created at all.

Change the line

LOG.debug(String.format("%s", arg));

to

LOG.debug("{}", arg);

[dbw9580]

/assign @YangchenYe323