Allow FELIX_DATASTORETYPE to fully control datastore type
Allow FELIX_DATASTORETYPE to fully control datastore type

(Without sometimes needing DATASTORE_TYPE or CALICO_DATASTORE_TYPE as
well.)

Metaswitch/calico,neiljerram/felix,Metaswitch/calico,neiljerram/felix,neiljerram/felix,neiljerram/felix