RFR: 8287398: Allow concurrent execution of hotspot docker tests [v2]

[Ioi Lam]

On Mon, 30 May 2022 07:04:11 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Okay, as long as multiple iterations of these tests pass.

I tested with `make test TEST=containers/docker JTREG="REPEAT_COUNT=50"` on a machine with 32 threads and it passed after 157 minuets.

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PR: https://git.openjdk.java.net/jdk/pull/8914