fix build on EPEL 7
    
    python-certbot-dns-route53 depends on python-boto3 which provides bundled
    versions of futures, jmespath, botocore but did not tweak its Python-level
    metadata accordingly (rhbz #1834529).
    
    "python setup.py test" uses that metadata and tries to download "missing"
    packages before collecting tests. This can be avoided by using pytest
    directly.
    
    The test case imports "boto3" first this will trigger an import of
    "boto.session" which makes the bundled libraries available.