Added mock as test dependency to Python2 environment

tox.ini

@@ -9,6 +9,10 @@ setenv = COVERAGE_FILE = .coverage
 commands = py.test --cov=fs_uae_wrapper --cov-report=term-missing
 deps = -r{toxinidir}/test-requirements.txt
 
+[testenv:py27]
+deps = {[testenv]deps}
+       mock
+
 [testenv:py34-flake8]
 basepython = python3.4
 deps = flake8