Add the exact cause of the exception while throwing/logging.

[PriyangaRamasamy]

In the whole project, wherever the exception is thrown, please check if the exact reason for the failure is thrown. Else add exception.what() wherever required.

eg: here, https://github.com/ibm-openbmc/openpower-vpd-parser/blob/P11_Dev/src/worker.cpp#L480
the message : "Json parsing failed" is not helpful in debugging. need to append ex.what() to know the exact cause of json parsing failure.