Update tox.ini file for coverage

1. Set basepython as 'python2.7'
2. Exclude tests files from coverage

Change-Id: I72834f76dd538f851cb457f2a4bf3c2b13ff70e7

tox.ini

@@ -32,10 +32,11 @@ commands =
   bandit -c bandit.yaml -r glare -n5 -p gate
 
 [testenv:cover]
+basepython = python2.7
 setenv = VIRTUAL_ENV={envdir}
 commands =
     coverage erase
-    python setup.py testr --coverage --testr-args='^(?!.*test.*coverage).*$'
+    python setup.py testr --coverage --testr-args='^(?!.*test.*coverage).*$' --omit="*/test*"
 
 [testenv:venv]
 commands = {posargs}