[NEW PORT] devel/py-pytest-cov: Pytest plugin for measuring coverage

[dbaio]

Summary

[NEW PORT] devel/py-pytest-cov: Pytest plugin for measuring coverage

This plugin produces coverage reports. It supports centralised testing and
distributed testing in both load and each modes. It also supports coverage of
subprocesses.

All features offered by the coverage package should be available, either through
pytest-cov or through coverage's config file.

WWW: https://github.com/pytest-dev/pytest-cov

Reviewed by:	koobs
Differential Revision:	D12394

Test Plan

$ portlint -CA
looks fine.

poudriere OK with Python 2.7 and 3.6.

10.3-RELEASE-p21 amd64
10.3-RELEASE-p21 i386
11.1-RELEASE-p1 amd64
11.1-RELEASE-p1 i386
12.0-CURRENT 1200044 amd64
12.0-CURRENT 1200044 i386

I didn't include a test target here because I wasn't able to get a satisfactory result.

do-test:
        @cd ${WRKSRC} && export TOXENV=py${PYTHON_SUFFIX} && tox -v

I had ~90% of success when I used the master branch from github (last commit).
With version 2.5.1 [2] I receive >95% of errors.

And is necessary all these dependencies:

devel/py-virtualenv
devel/py-tox
devel/py-cov-core
devel/py-fields (New port)
devel/py-aspectlib (New port)
devel/py-pytest-xdis
devel/py-pytest-cache
devel/py-helper (New port)
devel/py-yaml
devel/py-process-tests (New port)

IMHO it's not necessary a test target now, maybe in the next release.