Project: mesos
Issue MESOS-5668: Add CGROUP namespace to linux ns helper.
Since linux kernel 4.6, CGROUP namespace is added. we need to support the handle for the cgroup namespace of the process. This also relates to two test failures on Ubuntu 16: {noformat} [22:41:26] :	[Step 10/10] [ RUN ] NsTest.ROOT_setns [22:41:26] :	[Step 10/10] ../../src/tests/containerizer/ns_tests.cpp:75: Failure [22:41:26] :	[Step 10/10] nstype: Unknown namespace 'cgroup' [22:41:26] :	[Step 10/10] [ FAILED ] NsTest.ROOT_setns (1 ms) {noformat} {noformat} [22:41:26] :	[Step 10/10] [ RUN ] NsTest.ROOT_getns [22:41:26] :	[Step 10/10] ../../src/tests/containerizer/ns_tests.cpp:160: Failure [22:41:26] :	[Step 10/10] nstype: Unknown namespace 'cgroup' [22:41:26] :	[Step 10/10] [ FAILED ] NsTest.ROOT_getns (0 ms) {noformat}
Story points: 3