BUG-2470: add trace of failed modification

With this change, the InMemoryDOMDataStore trace logs should contain the
dump of failed modifications.

Change-Id: Iea3038169090a574030c5e03cf155089faa6e985
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-2470: add trace of failed modification"