problem to add values with status other than good

[joerg555]

If the status of a variable node is other than "good" you are not able to add the value to the datastore.

This is only a workaround to allow add variable with "uncertain" status.

Normaly you can allso have variable with "BADCOMMUNICATIONERROR" or other.
may be we have to change:

UA_DataValue
UA_Server_readWithSession(UA_Server *server, UA_Session *session,
                          const UA_ReadValueId *item,
                          UA_TimestampsToReturn timestampsToReturn);

to:

UA_StatusCode
UA_Server_readWithSession(UA_Server *server, UA_Session *session,
                          const UA_ReadValueId *item,
                          UA_TimestampsToReturn timestampsToReturn, UA_DataValue *dv)

to get full information with UA_DataValue and UA_StatusCode

Please check this, if you think it's the right way, i can change th code and make a pull request.