python-cryptography ftbfs in 18.04 LTS

according to
http://people.canonical.com/~doko/ftbfs-report/test-rebuild-20181222-bionic.html

python-cryptography ftbfs.

=================================== FAILURES ===================================
__________ TestOpenSSLMemoryLeaks.test_ec_private_numbers_private_key __________

self = <tests.hazmat.backends.test_openssl_memleak.TestOpenSSLMemoryLeaks object at 0x7f07f9dccf90>

    def test_ec_private_numbers_private_key(self):
        assert_no_memory_leaks(textwrap.dedent("""
            def func():
                from cryptography.hazmat.backends.openssl import backend
                from cryptography.hazmat.primitives.asymmetric import ec

                ec.EllipticCurvePrivateNumbers(
                    private_value=int(
                        '280814107134858470598753916394807521398239633534281633982576099083'
                        '35787109896602102090002196616273211495718603965098'
                    ),
                    public_numbers=ec.EllipticCurvePublicNumbers(
                        curve=ec.SECP384R1(),
                        x=int(
                            '10036914308591746758780165503819213553101287571902957054148542'
                            '504671046744460374996612408381962208627004841444205030'
                        ),
                        y=int(
                            '17337335659928075994560513699823544906448896792102247714689323'
                            '575406618073069185107088229463828921069465902299522926'
                        )
                    )
                ).private_key(backend)
> """))

../../../tests/hazmat/backends/test_openssl_memleak.py:216:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

s = "\ndef func():\n from cryptography.hazmat.backends.openssl import backend\n from cryptography.hazmat.primitives.... '575406618073069185107088229463828921069465902299522926'\n )\n )\n ).private_key(backend)\n"
argv = ['/usr/bin/python2.7', '-c', '\ndef func():\n from cryptography.hazmat.backends.openssl import backend\n from cr...n for ptr in remaining\n )))\n sys.stdout.flush()\n sys.exit(255)\n\nmain(sys.argv)\n']

    def assert_no_memory_leaks(s, argv=[]):
        env = os.environ.copy()
        env["PYTHONPATH"] = os.pathsep.join(sys.path)
        argv = [
            sys.executable, "-c", "{0}\n\n{1}".format(s, MEMORY_LEAK_SCRIPT)
        ] + argv
        # Shell out to a fresh Python process because OpenSSL does not allow you to
        # install new memory hooks after the first malloc/free occurs.
        proc = subprocess.Popen(
            argv,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
        )
        try:
            proc.wait()
            if proc.returncode == 255:
                # 255 means there was a leak, load the info about what mallocs
                # weren't freed.
                out = json.loads(proc.stdout.read().decode())
> raise AssertionError(out)
E AssertionError: {u'94745199970880': {u'path': u'../crypto/threads_pthread.c', u'line': 21, u'size': 56}, u'94745199970816': {u'path': u'../crypto/threads_pthread.c', u'line': 21, u'size': 56}}

../../../tests/hazmat/backends/test_openssl_memleak.py:111: AssertionError
============ 1 failed, 93357 passed, 4177 skipped in 448.23 seconds ============
E: pybuild pybuild:336: test: plugin distutils failed with: exit code=1: cd /<<PKGBUILDDIR>>/.pybuild/cpython2_2.7_cryptography/build; python2.7 -m pytest {dir}/tests/
dh_auto_test: pybuild --test -i python{version} -p 2.7 returned exit code 13
debian/rules:17: recipe for target 'build' failed
make: *** [build] Error 25