catapult: add a bit more documentation on how to use catapult tracing
Differential Revision: https://phab.mercurial-scm.org/D5217
catapult: introduce HGTESTCATAPULTSERVERPIPE to control run-tests' tracing
If unset, it will inherit its value from HGCATAPULTSERVERPIPE (which hg itself
also respects). By setting only HGTESTCATAPULTSERVERPIPE, we can get per-command
breakdowns of the test runtimes for the whole test suite without overloading the
trace file with the contents of the tracing from hg (such as demandimport, etc.)
Differential Revision: https://phab.mercurial-scm.org/D5216
catapult: rename 'active' to 'activetrace'; this isn't storing a boolean state
(This is an attempt to make it more obvious that the indentation is correct, to
prevent a repeat of
97f52862b1bd)
Differential Revision: https://phab.mercurial-scm.org/D5215