docker run error: ./env/bin/python: No such file or directory

docker run problem related to [use virtualenv by WyseNynja · Pull Request #340 · OpenBazaar/OpenBazaar](https://github.com/OpenBazaar/OpenBazaar/pull/340)

reporduce this issue

```
$ git clone https://github.com/OpenBazaar/OpenBazaar && cd OpenBazaar
$ docker build -t=test/ob .
$ docker run -i -t test/ob /bin/bash
# bash run.sh
...
run.sh: line 171: ./env/bin/python: No such file or directory
```