peer-or-repo: make sure object in "scheme" have a `instance` object
The previous form of having heterogeneous object in the dictionnary makes things
more complicated than they needed to be. I am not super happy about the current
(especially around 'islocal', that most item do not have), but this is already
much better.
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL