Add instance ID to commands that have to be executed within the lab directory

[ipspace]

Some netlab commands can be executed from anywhere as long as you supply the correct snapshot file. Others have to be executed within the lab directory.

Revisit all netlab commands, figure out which scenario applies to each of them, and add --instance parameter to those that have to be executed within the lab directory. The "within lab directory" commands should also use the path to the snapshot file as an indication they should change directory.

This will also remove considerations mentioned in #1628.