Strip trailing slash in file.directory state

Adding a trailing slash to the directory name (like /etc/chef/) would
fail the state if the directory didn't exist and `makedirs` was False.
This is because it would use os.path.dirname (which would return
/etc/chef) and see that the "parent" directory didn't exist, and fail.
Merge pull request #7713 from basepi/dirtrailingslash

Strip trailing slash in file.directory state