get_gis_type should work on remote datasets

[davemfish]

GDAL can open a connection to a remote file given a URL the same as for a local file, and easily retrieve metadata as from gdalinfo.

In pygeoprocessing, get_raster_info and get_vector_info take advantage of this, but get_gis_type does not, simply because it checks if the file exists on the local filesystem before trying to open it.