bitbake: fetch2: Ensure directory exists before creating symlink

If the mirrors code is trying to create a symlink and the
parent directory doesn't exist, as might be the case for sstate
mirrors where the fetch is into a subdir, it can silently fail.

Ensure the directory exists in this case to avoid issues.

(Bitbake rev: ff3afb1c1bb236c4a52c62a74f2917071e0af55b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit eff16e474ee7dc49ae433420a4c8d15d3314a618)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -1097,6 +1097,8 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
 
 def ensure_symlink(target, link_name):
     if not os.path.exists(link_name):
+        dirname = os.path.dirname(link_name)
+        bb.utils.mkdirhier(dirname)
         if os.path.islink(link_name):
             # Broken symbolic link
             os.unlink(link_name)