Import coastlines and land polygons into OSM db

* Using a manually and previously downloaded WGS84 coastline file from
http://openstreetmapdata.com/data/coastlines we populate a coastlines
table in OSM dbs
* Using a manually and previously downloaded WGS84 land polygon file from
http://openstreetmapdata.com/data/coastlines we populate a land_polygons
table in OSM dbs
* While at it, fix sysctl::parameter priority
* Rename osm::populatedb to osm::planet_import and move the shapefile
import functions to osm::shapefile_import
* Update docs and rspec tests

Change-Id: I457b92a8a9339a80874db3e7e13fc364fd8b0822
Merge "Import coastlines and land polygons into OSM db" into production