Take cpu for example, by default we expect gpdb dir to locate at
cgroup/cpu/gpdb.  But we'll also check for the cgroup dirs of init
process (pid 1), e.g. cgroup/cpu/custom, then we'll look for gpdb dir at
cgroup/cpu/custom/gpdb, if it's found and has good permissions, it can
be used instead of the default one.

If any of the gpdb cgroup component dir can not be found under init
process' cgroup dirs or has bad permissions we'll fallback all the gpdb
cgroup component dirs to the default ones.

NOTE: This auto detection will look for memory & cpuset gpdb dirs even
on 5X.

(cherry picked from commit f3dc101a)