Summary:
Main changes since 0.6.0:
  * cgroup properties collections (e.g. cgroup.controllers,
    cpu.weight, cpuset.cpus)
  * Support dumping with OpenMetrics format
  * Support dumping snapshots
  * Support specifying snapshot output file
  * memory.numa_stat collection
  * Various minor bugfixes

Reviewed By: lnyng

Differential Revision: D46912939

fbshipit-source-id: 8fbd8435918e76ff8cdcd2cc55144dd84fab9b7a