Make stdlib.getloadavg more resiliant.

Using rint(3) gave us a step where if one side was 1.4 and the other
was 1.5, that would be 1 and 2 respectively. So instead use a simple
difference. Also log more detail in case this doesn't fix the flakiness.

Bug: http://b/121156651
Test: ran tests
Change-Id: Ib5b2eb05d2b1eb8c4a10b182a8703510a3ef0cea