Add datastore properties to OS::Trove::Instance

Latest Trove supports datastore type and datastore version options
when creating Trove instances. This patch enables their usage in Heat.

Change-Id: I1d037a9fbf66f13c3195a55c7325d19b5e9a058c
Closes-bug: #1257690
Merge "Add datastore properties to OS::Trove::Instance"