bugfix: fix cgroup-parent can not set from config

[Ace-Tang]

remove initial value in cgroup-parent flag, or this flag
can never be set from config file when create container
with pouch cli.

Signed-off-by: Ace-Tang aceapril@126.com

Ⅰ. Describe what this PR did

func (mgr *ContainerManager) createContainerdContainer(ctx context.Context, c *Container) error {
    // CgroupParent from HostConfig will be first priority to use,
    // then will be value from mgr.Config.CgroupParent
    if c.HostConfig.CgroupParent == "" { 
        c.HostConfig.CgroupParent = mgr.Config.CgroupParent
    }    

If pouch cli give cgroup-parent a default value, the c.HostConfig.CgroupParent will never be empty, and it can never use CgroupParent set from daemon config file.

The default cgroup parent we already set in

    // same with containerd use. or make it a variable
    cgroupsParent := "default"
    if c.HostConfig.CgroupParent != "" {
        cgroupsParent = c.HostConfig.CgroupParent
    }   

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #1361 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #1361   +/-   ##
=======================================
  Coverage   17.34%   17.34%           
=======================================
  Files         189      189           
  Lines       11832    11832           
=======================================
  Hits         2052     2052           
  Misses       9633     9633           
  Partials      147      147

Impacted Files	Coverage Δ
cli/common_flags.go	0% <0%> (ø)	⬆️

[HusterWan]

Reasonable !!!, Thanks a lot @Ace-Tang

LGTM