Added unit tests for landsat 8 to test_landsat_dataset.py
Added unit tests for landsat 8 to test_landsat_dataset.py

These tests are for the extraction of metadata from landsat 8 datasets. No
tests yet for FC, since we do not yet have an example dataset.

smr547/agdc,GeoscienceAustralia/agdc,alex-ip/agdc,ama-jharrison/agdc,ama-jharrison/agdc,jeremyh/agdc,sixy6e/agdc,sixy6e/agdc,GeoscienceAustralia/agdc,jeremyh/agdc,smr547/agdc,alex-ip/agdc