gnu: python-pytest-cov: Use upstream options for testing.

* gnu/packages/python.scm (python-pytest-cov): Replace phase "check"
  by one passing the options found in upstream's tox.ini-file
  to "python setup.py check".

gnu/packages/python.scm

@@ -1662,6 +1662,16 @@ and many external plugins.")
          (base32
           "1yl4nbhzfgsxqlsyk4clafgp9x11zvgrkprm9i2p3fgkwx9jxcm8"))))
     (build-system python-build-system)
+    (arguments
+     `(#:phases
+       (modify-phases %standard-phases
+         (replace 'check
+          (lambda _
+            ;; options taken from tox.ini
+            ;; TODO: make "--restructuredtext" tests pass. They currently fail
+            ;; with "Duplicate implicit target name"
+            (zero? (system* "python" "./setup.py" "check"
+                            "--strict" "--metadata")))))))
     (propagated-inputs
      `(("python-coverage" ,python-coverage)
        ("python-pytest" ,python-pytest)))