It turns out that invalid JSON can be valid YAML ... thus if you mess
up a pkg-map file that still works as a YAML file dib-lint will let it
pass, but when pkg-map later tries to open it as a JSON file, it
fails.
Parse each type separately to catch these problems.
Change-Id: Ib3985e7d1599ed6bf3b7a73b786a53177b71fae0
8b4a5e9919