Add back some implicit imports where needed

- I took a gamble on how far we can go, now need to remedy
4 jobs for 111-explicit-relative in 1 minute and 38 seconds
Status Job ID Name Coverage
  Test
passed #2641
Go-py2.7

00:01:35

passed #2642
Go-py3.4

00:01:38

passed #2643
Go-py3.5

00:01:37

passed #2644
Go-py3.6

00:01:34