config-linux: clarify cgroupsPath
config-linux: clarify cgroupsPath

Clarify some of the confusion with cgroupsPath. Due to systemd, we
cannot require that relative paths be treated in any specific way. In
addition, add a line stating that not all values of cgroupsPath are
required to be valid (and that runtimes must error out if they have an
invalid cgroup path). However, any given value of cgroupsPath should
provide consistent results.

Signed-off-by: Aleksa Sarai <a8eb12d32d6ec07cdf737175ec7d4a0f1b4e1ee7@suse.de>

opencontainers/runtime-spec,cloudfoundry-incubator/specs,ujuc/specs,hqhq/runtime-spec,laijs/specs,hqhq/specs,wking/opencontainer-specs,wking/opencontainer-runtime-spec,vbatts/specs,opencontainers/specs,jonboulle/specs