sphinx-build in %build on EL7 produces an import error for the package being built

I'm trying to build some PyPI packages in Copr and while some build others fail in `%build` with such:

```
...
+ sleep 1
+ sphinx-build doc html
Making output directory...
Running Sphinx v1.1.3
Traceback (most recent call last):
File "generate_rst.py", line 5, in
import gevent
ImportError: No module named gevent
Exception occurred:
File "/builddir/build/BUILD/gevent-1.0.1/doc/conf.py", line 64, in
from gevent import __version__
ImportError: No module named gevent
```

As can be seen in this [log](https://copr-be.cloud.fedoraproject.org/results/brianjmurrell/manager-for-lustre-dependencies/epel-7-x86_64/00547024-python-gevent/build.log.gz) from this [package](https://copr.fedorainfracloud.org/coprs/brianjmurrell/manager-for-lustre-dependencies/package/python-gevent/).

I have enough that are failing like this that this must be a common problem, with a common solution?