run-tests: organize options into argument groups
And sort arguments so help output is more legible.
There are probably a ton of ways to group things. I tried to
picture the test harness as a pipeline and attempted to draw boundaries
around stages in that pipeline to create the groupings.
Differential Revision: https://phab.mercurial-scm.org/D1475
run-tests: convert to argparse
optparse has been deprecated since Python 3.2. Best to get on the new
boat before the old one sinks.
It looks like argparse formats its usage string differently than
optparse. Meh.
Differential Revision: https://phab.mercurial-scm.org/D1474