use venv pytest, stop using ancient mock version

dropping mock from the py3 reqs entirely so we use python's lib

test-requirements.txt

@@ -2,7 +2,6 @@
 defusedxml
 flake8
 flake8-import-order
-mock<=2.0.0
 requests-mock
 coverage
 pytest

tox.ini

@@ -36,7 +36,7 @@ commands_pre =
 [testenv:py3]
 deps =
     -r{toxinidir}/test-requirements.txt
-allowlist_externals = coverage3,pytest
+allowlist_externals = coverage3
 setenv = 
     {[testenv]setenv}
     PYTHONPATH=.:plugins/hub/.:plugins/builder/.:plugins/cli/.:cli/.:www/lib
@@ -44,7 +44,7 @@ commands_pre =
     {[testenv]commands_pre}
     coverage3 erase --rcfile .coveragerc3
 commands = 
-    pytest -n auto --cov --cov-config .coveragerc3 --cov-report=html
+    python -m pytest -n auto --cov --cov-config .coveragerc3 --cov-report=html
 
 [testenv:py2]
 deps =