bugfix: fix meta store return all item when empty prefix

[Ace-Tang]

meta store will return all items it keep if prefix is a empty
string.

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

Ⅰ. Describe what this PR did

 func (mgr *ContainerManager) Get(ctx context.Context, name string) (*Container, error) {
+       name = ""
        c, err := mgr.container(name)
        if err != nil {
                return nil, err

make name to empty, test

root@www:/var/lib/pouch# curl  -X GET --unix-socket /var/run/pouchd.sock "http:/containers/92b62b/json"
{"message":"container: : too many"}

it will return all container infos.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

unit test add.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #2104 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2104      +/-   ##
==========================================
+ Coverage   65.14%   65.15%   +0.01%     
==========================================
  Files         208      208              
  Lines       16407    16409       +2     
==========================================
+ Hits        10688    10691       +3     
  Misses       4388     4388              
+ Partials     1331     1330       -1

Flag	Coverage Δ
#criv1alpha1test	33.01% <0%> (-0.19%)	⬇️
#criv1alpha2test	33.83% <0%> (-0.01%)	⬇️
#integrationtest	39.77% <0%> (-0.11%)	⬇️
#unittest	23.9% <100%> (+0.06%)	⬆️

Impacted Files	Coverage Δ
pkg/meta/store.go	62.5% <100%> (+0.59%)	⬆️
apis/server/utils.go	61.9% <0%> (-4.77%)	⬇️
daemon/mgr/system.go	77.68% <0%> (-1.66%)	⬇️
cri/v1alpha1/cri.go	63.66% <0%> (-0.18%)	⬇️
daemon/logger/jsonfile/utils.go	73.17% <0%> (+1.62%)	⬆️
ctrd/image.go	78.94% <0%> (+1.75%)	⬆️

[allencloud]

I suggest that here we return an error, like return nil, fmt.Errorf("input prefix cannot be empty when getting object in store")

[allencloud]

LGTM