Set permissions on generated ring files

The use of NamedTemporaryFile creates rings with permissions 0600;
however most installs probably generate the rings as root but the
swift-proxy runs as user swift.

Set the permissions on the generated ring to 0644 prior to rename so
that the swift user can read the rings.

Change-Id: Ia511931f471c5c9840012c3a75b89c1f35b1b245
Closes-Bug: #1302700
Add tests and comments re constraints in /info

Add test to check that only the expected keys are
reported by proxy in /info, and add comments to
raise awareness that default constraints will be
automatically published by proxy in response to /info
requests.

Change-Id: Ia5f6339b06cdc2e1dc960d1f75562a2505530202
Merge "Add tests and comments re constraints in /info"
Merge "Set permissions on generated ring files"