Add tests for swift-ring-builder

Add some tests for essential methods in swift-ring-builder.
Tests for removing or changing device settings are executed
with different search values to cover many possible command
line arguments.

Currently tested methods:

- create ring
- add device
- remove device
- set weight
- set info
- set min_part_hours
- set replicas

Tests use swift.common.ring.RingBuilder to verify actions.

Catching and testing output from print statements is not
tested, because this requires redirecting sys.stdout during
tests and that might have some sideeffects for testing tools.

bin/swift-ring-builder has been moved to swift/cli/ringbuilder.py
and slightly modified to work as before (mainly due to no more
existing global variables since that part of the code has been
moved inside a main() function).

Change-Id: Ia63f59a8faca1fad990784f27532ca07a2125454
Fix a comment in SLO middleware

Change-Id: I6ef435db55eb6cac5a92d9ef0f7ac3eaf271761d
Merge "Add tests for swift-ring-builder"