Add support for passing environment variables to Cassandra process

[kpelykh]

I was looking for a way to pass ENV variable to Cassandra process, similar to EXECUTOR_ARG, however executor only passes JMX_PORT as a env variable to the process.

https://github.com/mesosphere/dcos-cassandra-service/blob/b407b9bc71870cf2c7d8d4b3c37dc5302154d2df/cassandra-executor/src/main/java/com/mesosphere/dcos/cassandra/executor/CassandraDaemonProcess.java#L254

Is there a plan to add such support? if it's not in your roadmap, would you be interested in PR for such feature?

[triclambert]

This repo is deprecated and will be archived in one week. Please see the latest version of Cassandra or DSE for DC/OS:

https://docs.mesosphere.com/service-docs/cassandra/
https://docs.mesosphere.com/service-docs/dse/ (enterprise-only)