Because initializing the texture can queue a copy from a staging
vk::Image, we must ensure we're not in a render pass. To make this
easier we move the current render pass tracking into the RendererVk
from the FramebufferVk class. (Note: in the future we will have
deferred command submission and this will become unnecessary.)

BUG=angleproject:2200

Change-Id: Ide8d4d70b50efbd79bbfa7006ad75cbc57cdf4c7
Reviewed-on: https://chromium-review.googlesource.com/741549
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>