Handle combined cpu,cpuacct cgroup mountpoints

[PaulFurtado]

Disclaimer: untested, need someone to get this built for me so we can test internally, but wanted to get the ball rolling.

On HubSpot's legacy systems, cgroups look like:

4:cpuacct:/hs_high_priority/mesos/83df193b-5cd3-4393-986a-f992dd284b03
3:cpu:/hs_high_priority/mesos/83df193b-5cd3-4393-986a-f992dd284b03

but on centos 8 systems, they look like:

2:cpu,cpuacct:/hs_high_priority/mesos/fb69d013-4e17-45fe-b47b-dde6a177a3a3

Parsers for /proc/pid/cgroup are supposed to split the subsystems field on , to determine which subsystems the line is for. Additionally, they should do a maxsplit of 3 to deal with cgroup names that may contain semicolons.

This PR should fix this error on CentOS 8 hosts:

java.lang.RuntimeException: Found no cpu cgroup from output [11:freezer:/hs_high_priority/mesos/f99d4218-bb4d-49f9-bd10-b47be89c3936, 10:devices:/system.slice/mesos-slave.service, 9:memory:/hs_high_priority/mesos/f99d4218-bb4d-49f9-bd10-b47be89c3936, 8:cpuset:/, 7:hugetlb:/, 6:blkio:/system.slice/mesos-slave.service, 5:net_cls,net_prio:/, 4:pids:/system.slice/mesos-slave.service, 3:perf_event:/, 2:cpu,cpuacct:/hs_high_priority/mesos/f99d4218-bb4d-49f9-bd10-b47be89c3936, 1:name=systemd:/hs_high_priority/mesos/f99d4218-bb4d-49f9-bd10-b47be89c3936]
        at com.hubspot.singularity.executor.SingularityExecutorCgroupCfsChecker.getCpuCgroupDirectory(SingularityExecutorCgroupCfsChecker.java:77)
        at com.hubspot.singularity.executor.SingularityExecutorCgroupCfsChecker.<init>(SingularityExecutorCgroupCfsChecker.java:53)
        at com.hubspot.singularity.executor.SingularityExecutorMonitor.lambda$startCgroupWatcher$0(SingularityExecutorMonitor.java:528)
        at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:829)

[WH77]

🚢