upgrade: prepare code (and output) for the idea of upgrading share This would work for a subset of action only. Our first target is dirstate-v2. Differential Revision: https://phab.mercurial-scm.org/D12196

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# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL