Shutdown function should never leave data behind

[iamemilio]

When explicitly calling the shutdown function, the expectation is that the execution of the code is being paused until all the data in queue is sent to NR1. This is not always the case, and sometimes longer harvest cycle data types like metrics can get left behind if the app shuts down before their harvest cycle. The shutdown should force a flush of all data that is queued for sending to NR1 by force.