Fix parsing of unicode filenames reported by git ls-files (#1339)

[phihos]

I fixed German umlauts in filenames by changing this

git ls-files '*.yaml' '*.yml'

to this

git ls-files -z '*.yaml' '*.yml'

The output in not delimited by newlines but by \0 instead. So I also had to change the output parsing.

A test case is included.

[phihos]

For the tests to pass with Python 3.6 I had to modify the test function run_ansible_lint to merge environment variables from the safe list to the _env var even if env in not None. Else variables like LANG are not passed and subprocess.call(...) tries to convert the unicode output to acii causing an error.

[ssbarnea]

Thanks for this PR, it really make me happy to review a pull-request that fixes a bug while explaining what and why. I am hoping to see more from you.