Reorder connectors checks
Reorder connectors checks

Reorders the check that the connector file exists with the check that
it's picked up by presto system catalog.  This will provide more helpful
information in case of failure.

Test Plan: Ran test_connector_add_remove

prestodb/presto-admin,Svjard/presto-admin,prestodb/presto-admin,Svjard/presto-admin