community/n2n: Fix default/single and multi instance setups

This fixes some issues with community/n2n-3.1.1-r0 (VPN):

1. service supernode stop doesn't work because of a missing foreground (-f) argument.
2. Additional edge/supernode instances (ln -s edge /etc/init.d/edge.second, ...) fail to start (supervise-daemon: /usr/sbin/edge is already running) because they use the same pidfile.
3. Starting/Stopping messages don't use instance names making it impossible to distinguish between them.
4. Config file names for the default/single instances are e. g. edge-edge.conf instead of edge.conf, complicating configuration management scripts expecting n2n config files in canonical places.

The commit just fixes some names in the edge and supernode init scripts. n2n sources are unaffected.