u/fjammes/dm-1497

PR for review.
Hi Andy, 

In my understanding a Dockerfile is used to create a VM image from scratch (or from an other vm image). I tried to launch two
`docker build --tag="jdoe/qserv:2014_10" - < Dockerfile` 
on the same machine at the same time, it has created two different VM images, which both contain /tmp/answers.txt. So I think it's not possible to have a conflict as it is not possible to use the same Dockerfile at the same in order to produce a unique image: two different images will be created

Am I clear?

Cheers,

Fabrice