bugfix: cgroup-parent must be abs

[HusterWan]

Signed-off-by: Michael Wan [email protected]

Ⅰ. Describe what this PR did

fix: if cgroup-parent is a relative path will not work on host.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

if cgroup-parent not specified both in client and daemon, the cgroupParent will be default (relative path). so if relative path not work on host , most of ci test will failed in cli_run_test.go.

but ci test like below works fine. it's wired

// TestRunWithCgroupParent tests running container with --cgroup-parent.
func (suite *PouchRunSuite) TestRunWithCgroupParent(c *check.C) {
	// cgroup-parent relative path
	testRunWithCgroupParent(c, "pouch", "TestRunWithRelativePathOfCgroupParent")

	// cgroup-parent absolute path
	testRunWithCgroupParent(c, "/pouch/test", "TestRunWithAbsolutePathOfCgroupParent")
}

so we should figure it out tomorrow @Letty5411

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #896 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #896      +/-   ##
==========================================
- Coverage   14.37%   14.37%   -0.01%     
==========================================
  Files         117      117              
  Lines        7103     7105       +2     
==========================================
  Hits         1021     1021              
- Misses       5995     5997       +2     
  Partials       87       87

Impacted Files	Coverage Δ
daemon/mgr/container.go	2.77% <0%> (-0.01%)	⬇️

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[HusterWan]

specify relative path for cgroup-path works different on centos and ubuntu, this pr can fix the difference

@allencloud @Letty5411 please TALA this pr

[Letty5411]

LGTM