Rename finishOpList to finishFlush and call it less frequently

Rename finishOpList to finishFlush and call it less frequently

It is expected that this will fix the Vulkan perf regression associated with splitting up the opLists

Change-Id: I1bbb6f71745bb08d4a8c2f7810e5ab84cca75e84
Reviewed-on: https://skia-review.googlesource.com/16901
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>