git: openjdk/jdk17u: master: 8274083: Update testing docs to mention tiered testing

[Aleksey Shipilev]

Changeset: 5e90da94
Author:    Aleksey Shipilev <shade at openjdk.org>
Date:      2021-10-04 14:54:12 +0000
URL:       https://git.openjdk.java.net/jdk17u/commit/5e90da94f4af225de1af8c0cd96c800a1924048b

8274083: Update testing docs to mention tiered testing

Backport-of: 971aa353aae51222ca33ebfdd61b91672a6c871a

! doc/testing.html
! doc/testing.md