RFR: 8265690: Use latest base image version in Docker testing

[Aleksey Shipilev]

On Wed, 21 Apr 2021 16:02:55 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Use latest image to get latest glibc, so that host-built JDK has a higher chance to pass. Current "oraclelinux:7.6" image apparently has glibc 2.27. Please see the bug for more discussion.
> 
> Additional testing:
>  - [x] `hotspot_containers` tests on Ubuntu 20.04 (glibc 2.31) -- used to fail, now passes
>  - [x] `hotspot_containers` tests on Debian 9 (glibc 2.24) -- continues to pass
>  - [x] `hotspot_containers` tests on Centos 7 (glibc 2.17) -- continues to pass

Turns out, the tests are throwing `SkippedException` on error. This masked the failure to resolve `oraclelinux:latest`... Looking at it a bit more.

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PR: https://git.openjdk.java.net/jdk/pull/3605