SERVER-13336 IndexUpdateTests: Only try to kill index builds

Now that counts can yield, they can be killed. The killAll() calls above were
not intended to effect the counts.

(cherry picked from commit 00c8264c88edbbda91c375063c2c612b1db18702)
Increase oplog size for test

(cherry picked from commit 192fd947da5ba99e4a06c769670b08cc9820f955)