fix node selection syntax to match logic in dbt-core

[drewbanin]

This PR changes the logic in is_selected_node to better match the implementation in dbt-core. I think I initially chose to set the ret value then return at the end of the implementation because i was using _.each() initially? The logic here now matches that of dbt-core exactly -- if each "selector part" matches the corresponding FQN part, then that node is a match. The GLOB selector part was previously required, but now it is optional.

Test it with:

staging.* == staging
marts.* == marts
marts.core.* == marts.core

closes #36