Fix tools/graduate.sh for work with directories

graduate.sh script works fine with files, but if we try create
new oslo library from existing directory, we get an
incorrect file structure.

For example if we run

 tools/graduate.sh foo openstack/common/foo/ tests/unit/test_foo/

We'll get file structure like

 oslo/foo/foo/file1.py

Added to graduate.sh `is directory` check to fix this issue.

Change-Id: Idd73288b12db54a44de14dbdef44fd8fd6617373
Documenting policy.json syntax

Adding some documentation about policy.json usage.

Change-Id: I4df6d470432d9d8cef8cf63d5cce8a995ef79516
Update wiki link in update.py

The old link doesn't exist anymore.

Change-Id: I88ef902c801d16330e535d065fe785724d4c3ba8
Merge "Documenting policy.json syntax"
Merge "Fix tools/graduate.sh for work with directories"
Merge "Update wiki link in update.py"