Functions like nmc_find_connection() and nmc_find_active_connection()
can easily find multiple matching results. For example, the
"connection.id" in NetworkManager is not enforced to be unique,
so if the user adds multiple connections with the same name,
they should be all selected.

The previous API had a @pos argument, that allowed to iterate over
the results. Change that, to return all matches in a GPtrArray.

Also, extend connection-show and other places, to anticipate that
a connection might be active multiple times in any moment.