running two benchs leads to have nested directory structure for the logs

[msimonin]

https://github.com/BeyondTheClouds/kolla-g5k/blame/92e4ab657b860b32e7d0bf801e25c9626658ea51/ansible/roles/bench/tasks/logs.yml#L7

a second call, will create a _data subdirectory instead of copying the contents.
As a result indexing the logs in the results vm will fail.

I suggest to

1. explicitly create /tmp/kolla-logs
2. explicitly copy the content of /var/lib/docker/volumes/kolla_logs/_data inside

subsequent call should overwrite previous ones, which is a more desirable behaviour.

[msimonin]

I think this is still present. Could we fix it ?