Instead of writing the CLI calls to stderr as INFO loglines, now add
them to a list of messages by prune/create/sync.
Always close the VPP connection after finishing, by adding a destructor
to the VPPApi class.
At the end of each phase, print out what was gathered to stdout. Later,
I will make this more advanced (output to file, output directly to a
pipe of a running vppctl binary, etc).
