--pyargs discovery for zipped packages/unpacked wheels/eggs

EDIT:

Using py.test --pyargs mypackage does not seem to work for .egg distributed packages.
Adding

[easy_install]
zip_ok = False

to setup.cfg seems to be a viable fix until py.test supports zipped packages.

Original issue text:

Using py.test --pyargs mypackage under a conda environment seems to be broken.
I've reported it here: https://github.com/conda/conda/issues/2075

I am reposting it here in case someone has an idea what might be going on here.
Here is a Dockerfile to reproduce the bug:

FROM continuumio/miniconda:3.19.0
MAINTAINER Björn Dahlgren <bjodah@DELETEMEgmail.com>
ENV PATH /opt/miniconda2/bin:$PATH
RUN git clone https://github.com/bjodah/dummypkg.git && \
    cd dummypkg && \
    conda install conda-build pytest && \
    conda build conda-recipe && \
    conda install --use-local dummypkg
RUN cd /tmp && \
    python -c 'import dummypkg; print(dummypkg.__file__)' && \
    python -m pytest --pyargs dummypkg

Running docker build generates the following output:

$ docker build revised-docker-environment/
Sending build context to Docker daemon 2.048 kB
Sending build context to Docker daemon 
Step 0 : FROM continuumio/miniconda:3.19.0
 ---> bc9d0fb804ac
Step 1 : MAINTAINER Björn Dahlgren <bjodah@DELETEMEgmail.com>
 ---> Using cache
 ---> f81cd6785b68
Step 2 : ENV PATH /opt/miniconda2/bin:$PATH
 ---> Using cache
 ---> 3227b31b6bd9
Step 3 : RUN git clone https://github.com/bjodah/dummypkg.git &&     cd dummypkg &&     conda install conda-build pytest &&     conda build conda-recipe &&     conda install --use-local dummypkg
 ---> Using cache
 ---> 6765cf1fae4d
Step 4 : RUN cd /tmp &&     python -c 'import dummypkg; print(dummypkg.__file__)' &&     python -m pytest --pyargs dummypkg
 ---> Running in e9c721e5c4c2
/opt/conda/lib/python2.7/site-packages/dummypkg-0.1.0-py2.7.egg/dummypkg/__init__.pyc
============================= test session starts ==============================
platform linux2 -- Python 2.7.10, pytest-2.8.5, py-1.4.31, pluggy-0.3.1
rootdir: /tmp, inifile: 

========================= no tests ran in 0.00 seconds =========================
ERROR: file or package not found: dummypkg
INFO[0000] The command [/bin/sh -c cd /tmp &&     python -c 'import dummypkg; print(dummypkg.__file__)' &&     python -m pytest --pyargs dummypkg] returned a non-zero code: 4 

Start by reproducing the failure with the linked Dockerfile and the python -m pytest --pyargs dummypkg command in the conda environment. Trace pytest's package discovery for the .egg path shown in the output; done means --pyargs discovers tests in zipped packages, unpacked wheels, or eggs instead of reporting that the package is not found.