//test:python3_coverage_test fails on FreeBSD #274

# ./pleasew test
18:39:17.868 WARNING: xattrs are not supported on this filesystem, using fallbacks
Fail: //test:python3_coverage_test   2 passed   0 skipped   0 failed   2 errored Took 350ms
Error: ImportError in test_can_import_tracer
cannot import name 'tracer' from 'coverage' (/root/python-rules/plz-out/tmp/test/python3_coverage_test._test/run_1/python3_coverage_test.pex/third_party/python/coverage/__init__.py)
Traceback (most recent call last):
  File "test/python_coverage_test.py", line 26, in test_can_import_tracer
    from coverage import tracer
ImportError: cannot import name 'tracer' from 'coverage' (/root/python-rules/plz-out/tmp/test/python3_coverage_test._test/run_1/python3_coverage_test.pex/third_party/python/coverage/__init__.py)

Error: ReturnValue in python3_coverage_test
Test returned nonzero but reported no errors
exit status 1
Standard output:

Running tests...
----------------------------------------------------------------------
.E.
======================================================================
ERROR [0.001s]: test_can_import_tracer (test.python_coverage_test.PythonCoverageTest.test_can_import_tracer)
Test we can import the binary tracer module.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test/python_coverage_test.py", line 26, in test_can_import_tracer
    from coverage import tracer
ImportError: cannot import name 'tracer' from 'coverage' (/root/python-rules/plz-out/tmp/test/python3_coverage_test._test/run_1/python3_coverage_test.pex/third_party/python/coverage/__init__.py)

----------------------------------------------------------------------
Ran 3 tests in 0.206s

FAILED (errors=1)

Generating XML reports...

//test:python3_coverage_test 4 tests run in 352ms; 2 passed, 2 errored
30 test targets and 61 tests run; 56 passed, 2 errored, 3 skipped.
Total time: 2.21s real, 2.82s compute.
Messages:
18:39:18.525   ERROR: //test:python3_coverage_test failed: Test returned nonzero but reported no errors