Osm land fixes

[gsoyka]

Updates to the osm_land and natural_earth importer scripts to handle use cases as follows:

• Case where osm_land and natural_earth databases are stored on different servers, with different sets of credentials.
• Case where we do not have permissions to drop existing natural_earth database

[ARolek]

@gsoyka this looks good, thanks for the PR. Can you please update the README under the Natural Earth and OSM Land sections with the new command flags?

[gsoyka]

@ARolek Good call, I've updated the readme with the various configuration scenarios

[ARolek]

Nice! Thank you.