remove log format type check

[oiooj]

Option LogConfig is omitempty in config. That means we allow c.HostConfig.LogConfig is nil.

There is no need to check the log type, we don't use it now in log sub command, maybe in the furture.

Fix #1105
Fix #1072

[pouchrobot]

@oiooj Thanks for your contribution. 🍻
Please sign off in each of your commits.

[pouchrobot]

ping @oiooj

CI fails according integration system.
Please refer to the CI failure Details button to corresponding test, and update your PR to pass CI.

If this is flaky test, welcome to track this with profiling an issue.

build url: https://travis-ci.org/alibaba/pouch/builds/370389143
build duration: 199s

[oiooj]

The circleCI need to be fixed.

package golang.org/x/lint: unrecognized import path "golang.org/x/lint" (parse https://golang.org/x/lint?go-get=1: no go-import meta tags ())

[HusterWan]

@oiooj The ci failed because golint download error, we will build a base image contains golint tool, in case network problem.

thanks a lot for your work !!!

[HusterWan]

LGTM