Add latlon to elevation error

[ASVincent]

Adds lat lon datum to elevation error message.

[sixy6e]

The next phase I'd like to incorporate a well known text representation (WKT) to report any geometry (should only be Points and Polygons that we deal with here).

eg

from shapely.geometry import Point, Polygon
p1 = Point((145.6, -33.7))
p2 = Polygon([(145.6, -33.7), (146.7, -33.7), (146.7, -34.8), (145.6, -34.8), (145.6, -33.7)])
print(p1.wkt)
'POINT (145.6 -33.7)'
print(p2.wkt)
'POLYGON ((145.6 -33.7, 146.7 -33.7, 146.7 -34.8, 145.6 -34.8, 145.6 -33.7))'

That way it'll be easy to build a vector file of all failed queries for a given job using a mixture of jq and python.

[sixy6e]

Current Region Of Interest (ROI) queries output the polygon as a wkt and attach it as an attribute to the dataset. So the ground work is there to enable the error reporting.

[sixy6e]

I restarted the Travis build. All tests now pass.

[sixy6e]

Ignore the extra request for the other ancillary lonlat if you haven't got to it. Merge in when you're ready.