--cover-min-percentage fails when only one module is included

[ngaya-ll]

Running nosetests with the --cover-min-percentage flag on a skeleton package with only an __init__.py file fails because the coverage output does not include a total line.

$ python setup.py nosetests --with-coverage --cover-min-percentage=80
running nosetests
running egg_info
...

Name               Stmts   Miss  Cover
--------------------------------------
my_package.py       0      0   100%
nose.plugins.cover: ERROR: No total percentage was found in coverage output, something went wrong.
----------------------------------------------------------------------
Ran 0 tests in 0.004s

OK