Open CDTDatastore's underlying TD_Database on -init
Open CDTDatastore's underlying TD_Database on -init

This helps to make sure initialisation code is only called
from one thread.

cloudant/CDTDatastore,cloudant/CDTDatastore,cloudant/CDTDatastore,phatblat/CDTDatastore,jhs/CDTDatastore,jimix/CDTDatastore,jhs/CDTDatastore,jimix/CDTDatastore,cloudant/CDTDatastore,jhs/CDTDatastore,phatblat/CDTDatastore,phatblat/CDTDatastore,jimix/CDTDatastore