Load constraints from cluster info dictionary

Use constrainst from the new "swift-constraints" section of test.conf,
fall back to those found in the response to the /info API call,
ultimately falling back to the constraints module's effective
constraints.

Change-Id: Iea01c9c4b5148faa10004a240df411cbe7336a6a
Fix error log of proxy-server when cache middleware is disabled

Change-Id: I0b67721cbb692fb8d2a5dd8b2c4f5383512b7b45
Closes-Bug: #1306591
setting request_node_count doesn't work

Change-Id: Ia161b872cf5ffa43c10334b42cc36d679c3adf56
Fix redundant add operation of set in ring

You don't need to add dev_id into seen_ids again when it has already existed in seen_ids.

Fixes Bug #1311190

Change-Id: If0766de8dc5e2a59a648cae39c789c91131805d2
Merge "Load constraints from cluster info dictionary"
Merge "setting request_node_count doesn't work"
Merge "Fix redundant add operation of set in ring"
Merge "Fix error log of proxy-server when cache middleware is disabled"
Fix several typos in the codebase.

These were found using https://github.com/intgr/topy

Change-Id: I0dc7b76c44b8b17b1dcd79184dad1516fb11173c