Revert "Use tempfile.tempdir for lock_path if OSLO_LOCK_PATH is not set"

This reverts commit 5021ef82fd.

That commit set default location for lock files to a world-writable
directory (like /tmp) which violates security precaution stated right in
the help string of lock_path config variable: lock_path should be
writable by the user of the process using it only.

There is some history behind this:

- when we decided to not do tempfile.mkdtemp if lock_path were not set
  (because it was broken), it broke upgrades for all components
  (starting with Cinder;
- it was suggested to provide the same default value:
  https://review.openstack.org/60274
  but it was not accepted because it weakens security;
- there was a thread about this in ML, please read it for more history:
  http://lists.openstack.org/pipermail/openstack-dev/2013-December/021055.html
  it ended up with understanding that only a project using the library
  can provide sane default value for lock_path, not the library itself.

Change-Id: I801004ad3c83862849696f00c6e7ca9877fd496b

oslo_concurrency/lockutils.py

@@ -41,14 +41,11 @@ _opts = [
                 help='Enables or disables inter-process locks.',
                 deprecated_group='DEFAULT'),
     cfg.StrOpt('lock_path',
-               default=os.environ.get("OSLO_LOCK_PATH", tempfile.gettempdir()),
+               default=os.environ.get("OSLO_LOCK_PATH"),
                help='Directory to use for lock files.  For security, the '
                     'specified directory should only be writable by the user '
                     'running the processes that need locking. '
                     'Defaults to environment variable OSLO_LOCK_PATH. '
-                    'If OSLO_LOCK_PATH is not set in the environment, use the '
-                    'Python tempfile.gettempdir function to find a suitable '
-                    'location. '
                     'If external locks are used, a lock path must be set.',
                deprecated_group='DEFAULT')
 ]