Don't raise GeoserverException on 404 occurrences when performing get_layergroup

[subaru-souders]

This relates to a recent bugfix made in PR #97.

When using the create_layergroup function, a get_layergroup call is made subsequently that raises a GeoserverException if the returned status is anything other than 200. Even though the create_layergroup function has a check to see if the layergroup already exists, the subsequent get_layergroup call will error out the program on a 404 code regardless, because the only passing scenario is, again, a 200 code.

If the only scenario in which a 404 code is returned is the result of a layergroup not existing (in this specific part of the code), could there be an additional check for 404 codes?

[iamtekson]

The related PR is already merged. I will close this issue for now!