AArch64: fix golint error on ARM CI.

[Pennyzct]

Description of problem

Recently, ARM CI frequently failed on the following golint error:
http://jenkins.katacontainers.io/job/kata-containers-runtime-ARM-18.04-PR/1451/console

11:24:18 pkg/rootless/rootless.go:57:2: comment on exported var `IsRootless` should be of the form `IsRootless ...` (golint)
11:24:18 	//The function is declared this way for mocking in unit tests
11:24:18 	^
11:24:23 Build step 'Execute shell' marked build as failure

Updates:
New error output:

12:13:45 # Gopkg.lock is out of sync:
12:13:45 github.com/opencontainers/runc/libcontainer/system: imported or required, but missing from Gopkg.lock's input-imports

It looks like that in PR #2418, we imported github.com/opencontainers/runc/libcontainer/system, but forgot to dep ensure ?

[Pennyzct]

/test

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@a91cb13). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2435   +/-   ##
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  Coverage          ?   50.88%           
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  Files             ?      112           
  Lines             ?    16157           
  Branches          ?        0           
=========================================
  Hits              ?     8222           
  Misses            ?     6922           
  Partials          ?     1013

[Pennyzct]

/test

[Pennyzct]

Hi~~ guys
ARM CI is finally green again.🎉
Power8 and initrd CI have all failed on the same error and should be irrelevant with this PR:

./rootfs-builder/rootfs.sh: line 280: /tmp/jenkins/workspace/kata-containers-runtime-ubuntu-18-04-PR-initrd/go/src/github.com/kata-containers/osbuilder/rootfs-builder/*default-initrd-name/config.sh: No such file or directory
Failed at 120: sudo -E AGENT_INIT="${AGENT_INIT}" AGENT_VERSION="${agent_commit}" GOPATH="$GOPATH" USE_DOCKER=true

We have already raised #2431 and kata-containers/tests#2275 to try to fix them. ;).

[grahamwhaley]

lgtm