Firmware takes more time to boot the more log files there are on the SD card

[selimnairb]

Original report by Brian Miles (Bitbucket: [Brian Miles](https://bitbucket.org/Brian Miles), ).

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I was working with a Nemo 30 logger that had ~100 log files on it. The logger took about 5 minutes to finish booting (i.e., I can connect via the Wifi AP and use the configuration website). I tried the same logger with an empty SD card and it finishes booting un just a few seconds. The LogManager code should be reviewed to see if the boot time can be reduced or ideally be made constant regardless of how many log files there are on the SD card.