cassandra: Increase stack size to fix startup

The lastest JVM in osv.git refuses to start up an application with 180k
stack size.  Bump it up to the required minimum to make Cassandra start
up again.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Merge pull request #2 from penberg/cassandra-stack-size

cassandra: Increase stack size to fix startup