EC GET path: require fragments to be of same set

And if they are not, exhaust the node iter to go get more.  The
problem without this implementation is a simple overwrite where
a GET follows before the handoff has put the newer obj back on
the 'alive again' node such that the proxy gets n-1 fragments
of the newest set and 1 of the older.

This patch bucketizes the fragments by etag and if it doesn't
have enough continues to exhaust the node iterator until it
has a large enough matching set.

Change-Id: Ib710a133ce1be278365067fd0d6610d80f1f7372
Co-Authored-By: Clay Gerrard <clay.gerrard@gmail.com>
Co-Authored-By: Alistair Coles <alistair.coles@hp.com>
Closes-Bug: 1457691

test/probe/test_reconstructor_revert.py

@@ -21,7 +21,7 @@ import random
 import shutil
 from collections import defaultdict
 
-from test.probe.common import ECProbeTest
+from test.probe.common import ECProbeTest, Body
 
 from swift.common import direct_client
 from swift.common.storage_policy import EC_POLICY
@@ -31,32 +31,6 @@ from swift.obj import reconstructor
 from swiftclient import client
 
 
-class Body(object):
-
-    def __init__(self, total=3.5 * 2 ** 20):
-        self.total = total
-        self.hasher = md5()
-        self.size = 0
-        self.chunk = 'test' * 16 * 2 ** 10
-
-    @property
-    def etag(self):
-        return self.hasher.hexdigest()
-
-    def __iter__(self):
-        return self
-
-    def next(self):
-        if self.size > self.total:
-            raise StopIteration()
-        self.size += len(self.chunk)
-        self.hasher.update(self.chunk)
-        return self.chunk
-
-    def __next__(self):
-        return next(self)
-
-
 class TestReconstructorRevert(ECProbeTest):
 
     def setUp(self):