The docker tests in //tools/cpp/test still assume that the sources
are enough to just compile.sh to bootstrap a bazel binary. Fix this,
by using the distribution archive instead.

While there, also add a target for the distribution archive as tar.

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Change-Id: Ic31bb95da0165f83a14537a1719c27e5067d0d65
Reviewed-on: https://cr.bazel.build/7531
MOS_MIGRATED_REVID=140134322