Revert "[swarming] enable test_priority"
Revert "[swarming] enable test_priority"

This reverts commit 05dbccca3ce6e3fa58983e77558a7caee2c7db15.

Reason for revert: it failed frequently on https://crrev.com/c/2303233.

Original change's description:
> [swarming] enable test_priority
> 
> I tried 4 times, but the test didn't fail.
> 
> https://ci.chromium.org/p/infra/builders/try/luci-py-try-xenial-64/b8874723571879606864?
> https://ci.chromium.org/p/infra/builders/try/luci-py-try-xenial-64/b8874725102777434800?
> https://ci.chromium.org/p/infra/builders/try/luci-py-try-xenial-64/b8874725847201216960?
> https://ci.chromium.org/p/infra/builders/try/luci-py-try-xenial-64/b8874727032138871360?
> 
> Bug: 1010816
> Change-Id: Ibdca66e72c33741598e48a8aa9872b8c7db6c0ab
> Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2299163
> Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
> Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
> Reviewed-by: Takuto Ikuta <tikuta@chromium.org>

TBR=tikuta@chromium.org,aaef61ef98ffea505db831f310be2a0eb8492537@google.com,yekuang@google.com,infra-scoped@luci-project-accounts.iam.gserviceaccount.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1010816
Change-Id: Id9c1e90de6a5ae389b767fe46b6f2e460e639d30
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2305824
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py