fix: confirm initial database connectivity (#314)

- adding db.Ping() call to confirm actual connection to the database to
  report issues with connectivity as early as possible

Co-authored-by: Kyle Johnson <kjohnson@gnulnx.net>

postgresql/config.go

@@ -277,6 +277,10 @@ func (c *Client) Connect() (*DBConnection, error) {
 		} else {
 			db, err = postgres.Open(context.Background(), dsn)
 		}
+
+		if err == nil {
+			err = db.Ping()
+		}
 		if err != nil {
 			errString := strings.Replace(err.Error(), c.config.Password, "XXXX", 2)
 			return nil, fmt.Errorf("Error connecting to PostgreSQL server %s (scheme: %s): %s", c.config.Host, c.config.Scheme, errString)