Fixes `sum(memoryAllocatable)` and `sum(podAllocatable)`. These
previously tested the wrong resource (cpuAllocatable).
Also refactor comparison functions to unify resolving properties and add
more testing.
Fixes#179.
Remove repetition across test cases that made it hard to read. Tweaks
tests where needed so they can all use the same node data. Also corrects
a test where the description didn't match the test.