Fix coverage for IPA

ironic-python-agent coverage was broken, tox -ecover printed error
messages. This change fixes the coverage command to work reliably, and
adds the directory generated by the job to gitignore.

Change-Id: I36656c17c13b5b4bce8e7eca2ec0f12c1bf76f29

.gitignore

@@ -7,6 +7,7 @@ ChangeLog
 *.egg
 .tox/*
 devenv/*
+cover
 .coverage
 coverage.xml
 .testrepository

tox.ini

@@ -35,7 +35,7 @@ commands =
 [testenv:cover]
 setenv = VIRTUAL_ENV={envdir}
 commands =
-  python setup.py testr --coverage {posargs:ironic_python_agent}
+  python setup.py test --coverage --coverage-package-name ironic_python_agent {posargs}
 
 [testenv:venv]
 setenv = PYTHONHASHSEED=0