do not log stack trace for CacheException reporting disabled cache an…

[vladak]

This change removes superfluous stack trace from the log entry in the case of disabled annotation cache by adding a property to CacheException and performing the logging based on this property.

The alternative would be to change the code in HistoryGuru#createAnnotationCache() and avoid throwing the exception in such case however that would impact testability. Or, try to use a hack and set the elements of the exception object via setStackTrace() which seems fragile (if it actually works in this case).

Example of the changed log entry:

15:06:23 FINER: failed to create annotation: repository {dir='/var/opengrok/src.linux/linux',type=git,historyCache=on,renamed=false,merge=true,annotationCache=off} does not allow to create annotation cache for '/var/opengrok/src.linux/linux/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml'
15:06:23 FINEST: Added: '/linux/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml' (YamlAnalyzer) (took 8 ms)

While there, I fixed some related and not so related nits.