verify: use some intermediate variables instead of a multi-liner This is shorter and easier to read as the indentation remains the same. Differential Revision: https://phab.mercurial-scm.org/D10818

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# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL