with_tree recursive filename lookup plugin.

This uses os.walk to return the names of all files (but not dirs) recursively
under a given directory.  Relative paths remain relative (to the playbook dir),
to facilitate copying a tree of files to a different location on the remote
host (absolute paths stay absolute).  A list of starting directories can be
given (no attempt is made to eliminate duplicates).  An optional 'filter' kwarg
gives an (fnmatch) shell glob for the filenames to return.  An optional
'followlinks' kwarg specifies whether to descend into directory links (true by
default; no attempt is made to avoid infinite loops). This modifies the copy
module to create all directories under the file being copied.  When used with
copy, it does not copy empty directories (as there are no files to return).