test: preserve the existing module policy config for testrepohg resuse
The test runner is, righfully, setting HGMODULEPOLICY to match the flavor
requests to run the tests. However this mess with the `testrepohg` ability to
run properly, as the newly set policy might be incompatible with its
installation, or its ability to read the test repo.
So we preserve the initial value in a dedicated variable and use it in the
`testrepohg` helper.
# Blacklist for a full testsuite run with fsmonitor enabled.
# Used by fsmonitor-run-tests.
# The following tests all fail because they either use extensions that conflict
# with fsmonitor, use subrepositories, or don't anticipate the extra file in
# the .hg directory that fsmonitor adds.
#### mainly testing eol extension
test-eol-add.t
test-eol-clone.t
test-eol-hook.t
test-eol-patch.t
test-eol-tag.t
test-eol-update.t
test-eol.t
test-eolfilename.t
#### mainly testing largefiles extension
test-issue3084.t
test-largefiles-cache.t
test-largefiles-misc.t
test-largefiles-small-disk.t
test-largefiles-update.t
test-largefiles-wireproto.t
test-largefiles.t
test-lfconvert.t
#### mainly testing nested repositories
test-nested-repo.t
test-push-warn.t
test-subrepo-deep-nested-change.t
test-subrepo-recursion.t
test-subrepo.t
#### fixing these seems redundant, because these don't focus on
#### operations in the working directory or .hg
test-debugextensions.t
test-extension.t
test-help.t