Change datadir for avoid failure due to lost+found

[mrkm4ntr]

I try to run katib on GKE, but vizier-db cannot start with following error.

Initializing database
2019-03-14T07:13:42.050153Z 0 [Note] Basedir set to /usr/
2019-03-14T07:13:42.050470Z 0 [Warning] The syntax '--symbolic-links/-s' is deprecated and will be removed in a future release
2019-03-14T07:13:42.051712Z 0 [ERROR] --initialize specified but the data directory has files in it. Aborting.
2019-03-14T07:13:42.051812Z 0 [ERROR] Aborting

It is due to lost+found directory in mounted path.

This PR is a same solution as below.
https://github.com/kubeflow/kubeflow/blob/4e6c645eeee0915999c33bf6772d2a996cb55ee4/kubeflow/katib/vizier.libsonnet#L303-L306

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This change is 

[k8s-ci-robot]

Hi @mrkm4ntr. Thanks for your PR.

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[YujiOshima]

/ok-to-test

[hougangliu]

/lgtm
/approve

[k8s-ci-robot]

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