linters: lint that library files don't start with #!

See notes in I4e6e85156459cca032e6c3e1d8a9284be919ccca, this ensures
the library files don't start with #! so they will run under the
Ansible interpeter on the remote node.

Change-Id: I8754d0962e8453d2030c589be23560e454e0052e

tox.ini

@@ -46,6 +46,7 @@ deps =
   -r{toxinidir}/linters-requirements.txt
 
 commands =
+  bash -c "for f in $(find . -path './roles/*/library/*.py' | xargs); do echo Checking shebang on $f; if head -1 $f | grep -q '^#!'; then echo $f 'starts with #!, it should not as Ansible will choose the interpreter'; exit 1; fi; done"
   flake8 {posargs}
   yamllint -s -f parsable .
   python -m ansiblelint --version