Docker script to build netcdf4-python and run 32-bit tests

See: https://gist.github.com/731ad9c3c96da2106ebf36fb6f4b073b

```
docker run --rm -ti -v $PWD:/io matthewbrett/trusty:32 /bin/bash
```

then in the container:

```
source /io/install_netcdf4.sh
```