Fix has_table method (#3741)
Fix has_table method (#3741)

Dialect's has_table method requires connection as the first argument, not engine (https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/engine/interfaces.py#L454). Instead, we can use engine's has_table method that handles the connection for us (https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/engine/base.py#L2141). Alternatively, we could call engine.dialect.has_table(engine.connect(), ...).
apache/incubator-superset,dmigo/incubator-superset,airbnb/superset,zhouyao1994/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,dmigo/incubator-superset,airbnb/caravel,mistercrunch/panoramix,airbnb/caravel,airbnb/caravel,dmigo/incubator-superset,timifasubaa/incubator-superset,timifasubaa/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,apache/incubator-superset,airbnb/superset,alanmcruickshank/superset-dev,alanmcruickshank/superset-dev,alanmcruickshank/superset-dev,mistercrunch/panoramix,alanmcruickshank/superset-dev,airbnb/superset,apache/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,airbnb/superset,timifasubaa/incubator-superset,mistercrunch/panoramix,apache/incubator-superset,zhouyao1994/incubator-superset,mistercrunch/panoramix,dmigo/incubator-superset