Fix the 'cover' tox env

currently tox env for code coverage does not measure anything
as it tries to measure the coverage of 'ironic-staging-drivers' package,
while the actual package name is 'ironic_staging_drivers'.

This patch:
- erases current coverage data first
- fixes project name expected by 'coverage'
- adds coverage reporting in the end of 'tox -ecover' run
- omits tests file from both coverage and report
- adds 'cover' to .gitignore (auto-generated as part of coverage report)

Change-Id: I0044e3dd399934be706a06fd921972632efcceea

.gitignore

@@ -24,6 +24,7 @@ pip-log.txt
 
 # Unit test / coverage reports
 .coverage
+cover
 .tox
 nosetests.xml
 .testrepository

tox.ini

@@ -26,7 +26,10 @@ commands =
 commands = {posargs}
 
 [testenv:cover]
-commands = python setup.py test --coverage --testr-args='{posargs}'
+commands =
+    coverage erase
+    python setup.py test --coverage --omit '*test*' --coverage-package-name ironic_staging_drivers --testr-args='{posargs}'
+    coverage report --omit='*test*'
 
 [testenv:docs]
 commands = python setup.py build_sphinx