Fix recursive glob on MockFs

Recursive globs on MockFs were ending up in an unmocked os.Lstat
call in walkAllDirs.  Move walkAllDirs into the FileSystem interface
as ListDirsRecursive.

Also duplicate the glob tests on both the real filesystem and on
MockFs.

Test: glob_test.go
Change-Id: Ia6b6b5eecdd17955a49d684a0fd5e55df05cfe62