No Suitable Driver when dynamically loading hive-jdbc jar

I'm trying to use the Hive JDBC drivers to connect to Impala, but getting "No Suitable Driver"

Similar to the SQL Tutorial ... in my SQL notebook cells:
1. `%classpath add jar /tmp/hive-jdbc-2.3.2-standalone.jar`
2. `%defaultDatasource impala=jdbc:hive2://:21050/default`
3. `SELECT 1;`
`com.twosigma.beakerx.sql.DBConnectionException: Connection URI:impala=jdbc:hive2://:21050/default; No suitable driver`

When I run %classpath, it lists the hive jar as expected. I'm using the hive-jdbc [shaded standalone jar](http://central.maven.org/maven2/org/apache/hive/hive-jdbc/2.3.2/). I see the work done in #6222 and #6223 to dynamically load drivers, so looks like this should work. Any suggestions on what to try next, or other known issues with dynamically loading JDBC drivers?

Environment: BeakerX 0.12.0, Jupyter 4.4.0, Conda Python 3.6.4, CentOS 6.9

Thanks!