Securely create signing_dir (bug 1174608)

Also verifies the security of an existing signing_dir.

Change-Id: I0685b4274a94ad3974a2b2a7ab3f45830d3934bb
(cherry picked from python-keystoneclient 1736e2ffb12f70eeebed019448bc14def48aa036)
(cherry picked from commit 24c25b38ed6fc95ed919ab34463cdb10bdcc57fd)
Revoke tokens on user delete (bug 1166670)

Change-Id: I8dacf71b43cffc12439520e05918729e385cb60a