Fix race condition in fileserver cache

This uses os.mkdir which is hopefully atomic and cross-platform. I'd
like to thank http://pythonhosted.org/lockfile/ for that idea.

Conflicts:
	salt/fileserver/__init__.py

Conflicts:
	salt/fileserver/__init__.py
Fix whitespace for salt-jenkins
Merge pull request #9907 from mbirtwell/fix_fileserver_cache_race_2014_1

Fix fileserver cache race 2014 1