Use DataValueFactory::tryNewFromArray in legacy SnakSerializer

This allows invalid values to properly be deserialized as
UnDeserializableValue, in case of an error.

Change-Id: Ie7bd3a02289aedd75a617c15bd78ad21f33c158a
Use invalid UnDeserializableValue in DataModelSerializationRoundtripTest

instead of value => 'a string!', type => 'string' which can be deserialized
back into StringValue, use type => 'time' so we can verify this comes
back correctly as UnDeserializableValue in the roundtrip tests.

also add @group Wikibase to DataModelSerializationRoundtripTest so
that the tests actually run on jenkins and travis!

Change-Id: Ifc8892cf313c63d7c76036d2ebf069c438add481
Merge "Use DataValueFactory::tryNewFromArray in legacy SnakSerializer"
Merge "Use invalid UnDeserializableValue in DataModelSerializationRoundtripTest"