Make error limits survive a ring reload

The proxy was storing the error count and last-error time in the
ring's internal data, specifically in the device dictionaries. This
works okay, but it means that whenever a ring changes, all the error
stats reset.

Now the error stats live in the proxy server object, so they survive a
ring reload.

Better yet, the error stats are now keyed off of the node's
IP/port/device triple, so if you have the same device in two rings
(like with multiple storage policies), then the error stats are
combined. If the proxy server sees a 507 for an objec request in
policy X, then that will now result in that particular object disk
being error-limited for requests in policies Y and Z as well.

Change-Id: Icc72b68b99f37367bb16d43688e7e45327e3e022
Handle os.listdir failures in object-updater

While investigating bug 1375348 I discovered the problem
reported there was not limited to the object-auditor.  The
object-updater has similar bugs.

This patch catches the unhandled exception that can be thrown
by os.listdir if the self.devices directory is inaccessible.

Change-Id: I6293b840916bb63cf9eebbc05068d9a3c871bdc3
Related-bug: 1375348
Remove invalid connection checking in db_replicator

Account/Container-replicator checks connection generation and timeout
in HTTP REPLICATE Request in _repl_to_node, but it doesn't really checks
connection but only construction of ReplConnection class.
This patch removes that invalid checking.

Change-Id: Ie6b4062123d998e69c15638b741e7d1ba8a08b62
Closes-Bug: #1359018
Correct misspelled words

In some files I found misspelling words.

bin/swift-reconciler-enqueue#l26
   primarly => primarily
swift/account/backend.py#l309
   ommited => omitted
swift/container/replicator.py#l158
   successfull => successful
test/unit/account/test_backend.py#1450
   non_existant_policy_index => non_existent_policy_index
test/unit/account/test_backend.py#1451
   'test-non-existant-policy'=> 'test-non-existent-policy'
test/unit/account/test_backend.py#1453
   non_existant_policy_index => non_existent_policy_index

Change-Id: I976236e3200a6fbdc20be464acff182b6cface81
Merge "Remove invalid connection checking in db_replicator"
Merge "Handle os.listdir failures in object-updater"
Merge "Make error limits survive a ring reload"