Update hive2.xml

Adding hint about the using the new connection url to be used with database names that are other than default with Hive when using JDBC driver <= 0.12
TEIID-2878 pushing limit/order by over union
TEIID-2358 completely resetting join strategy state
TEIID-2870 expanding the allow-join property
TEIID-2886 lowering the max number of dependent join values that can be
pushed