Changes

gather-topology: gather cgroup2 mount point
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

linux: use /proc/<pid>/cpuset before proc/<pid>/cgroup
cgroup is much harder to parse, and even worse with cgroups v2, use
cpuset whenever possible.
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

linux: prepare /proc/<pid>/cgroup parsing for cgroups v2
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

linux: cleanup the switching between cgroup1 and cpuset mount points
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

linux: add support for cgroup v2
v2 cgroups use a unified hierarchy for all controllers, where a parent
can restrict to something different than a child. We must use the
"effective" cpus and mems masks to get the actual intersection of all
restrictions.
v1 and v2 cgroups may coexist, we check the v2 controllers to see if
"cpuset" is enabled there, or look for v1 with a cpuset options, or for
the old "cpuset" alias.
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

tests/linux: add a non-cpuset cgroup2 to
16amd64-4n4c-cgroup-distance-merge
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

tests/linux: change 32amd64-4s2n4c-cgroup to cgroup2
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>