venv: adapt requirements for python3

We disable the coverage logic as it doesn't seem critical and it
doesn't work right under python3 due to missing wheels.  We can
re-add it if needed after more investigation.

BUG=chromium:1052692
TEST=CQ passes

Change-Id: Id4d0a6df343cacc3f5773fb46f1995c74bc5474a

venv/pytest.ini

diff --git a/venv/pytest.ini b/venv/pytest.ini
index 060586e..64f9f23 100644
--- a/venv/pytest.ini
+++ b/venv/pytest.ini
@@ -3,4 +3,5 @@
   --doctest-modules
   --durations=5
   --ignore setup.py
-  --cov cros_venv
+# TODO: Turn back on when we have Python 3 wheels.
+#  --cov cros_venv

venv/requirements.txt

diff --git a/venv/requirements.txt b/venv/requirements.txt
index 58dcdb8..90219cc 100644
--- a/venv/requirements.txt
+++ b/venv/requirements.txt
@@ -1,12 +1,12 @@
-coverage==4.4.1
+coverage==4.4.1; python_version < '3'
 funcsigs==1.0.2
 mock==2.0.0
 pbr==1.10.0
 pip==8.1.2
 py==1.4.34
 pytest==3.1.3
-pytest-cov==2.5.1
+pytest-cov==2.5.1; python_version < '3'
 setuptools==28.2.0
 six==1.10.0
-subprocess32==3.2.7
+subprocess32==3.2.7; python_version < '3.3'
 wheel==0.30.0