Add skip_install in non-testing tox envs and py35

Author: Lee Miller

tox.ini

@@ -15,6 +15,7 @@ commands =
     coverage run -a -m tests
 
 [testenv:lint-basic]
+skip_install = true
 basepython = python3
 deps =
     bandit
@@ -38,11 +39,16 @@ commands = python setup.py build_sphinx
 skip_install = true
 commands = python pybitmessage/bitmessagemain.py -t
 
+[testenv:py35]
+skip_install = true
+
 [testenv:reset]
+skip_install = true
 deps = coverage
 commands = coverage erase
 
 [testenv:stats]
+skip_install = true
 deps = coverage
 commands =
     coverage report