Filter out unavailable databases (#3875)
Filter out unavailable databases (#3875)


zhouyao1994/incubator-superset,timifasubaa/incubator-superset,dmigo/incubator-superset,mistercrunch/panoramix,airbnb/caravel,airbnb/caravel,airbnb/superset,apache/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,apache/incubator-superset,apache/incubator-superset,airbnb/superset,timifasubaa/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,dmigo/incubator-superset,airbnb/superset,apache/incubator-superset,airbnb/superset,mistercrunch/panoramix,zhouyao1994/incubator-superset,zhouyao1994/incubator-superset,dmigo/incubator-superset,mistercrunch/panoramix,mistercrunch/panoramix,airbnb/caravel,apache/incubator-superset,dmigo/incubator-superset