Omit tests from code coverage run

Fine-tune the coverage results by:
  - Omitting the tests folder from the coverage run.
  - Added report generation of coverage on the console while tox
    target run.
  - Removed and consolidated duplicate switches from run/report
    commands inside .coveragerc file, which was already present.

Change-Id: I5c44e73768487eaefebf95f1dd026ba99b90a04c

.coveragerc

@@ -1,9 +1,13 @@
 [run]
 branch = True
 source = sushy
+omit =
+    *tests*
 
 [report]
 ignore_errors = True
+omit =
+    *tests*
 
 [html]
 directory = cover

tox.ini

@@ -27,14 +27,15 @@ commands = {posargs}
 basepython = python3
 setenv =
    {[testenv]setenv}
-   PYTHON=coverage run --source sushy --parallel-mode
+   PYTHON=coverage run --parallel-mode
 # After running this target, visit sushy/cover/index.html
 # in your browser, to see a nicer presentation report with annotated
 # HTML listings detailing missed lines.
 commands = coverage erase
            stestr run {posargs}
            coverage combine
-           coverage html -d cover
+           coverage report
+           coverage html
            coverage xml -o cover/coverage.xml
 
 [testenv:docs]