Fixes an issue with the XMLEquals matcher

The matcher implementation would fail to match two documents that are
semantically equivalent, but sibling elements appear in different
document order.

Change-Id: I99dc6401e73be4c61bb265c3258b6245f2e7bb34
Closes-bug: #1347891
Merge "Fixes an issue with the XMLEquals matcher" into stable/icehouse
Merge remote-tracking branch 'upstream/stable/icehouse' into stable/icehouse