Use pickle to save cache to temporary disk
Use pickle to save cache to temporary disk

When developing it is handy to have a cache stored in a temporary file
that can be quickly reloaded when restarting the app. Use pickle to dump
the cache to file so that it can be reread at boot if it exists.

Change-Id: I8638584914ec54ef6523449684ad72b4ec02b72b
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer