Need to add new session settings for Drill-MapRDB plugin

[Smidth Panchamia]

Hello,

I wanted to add new session variables that would be recognized only by the
drill-MapRDB JSON plugin.

Is there a way to add these only through the plugin code(which lies outside
of drill codebase)?

If not, here is the change I have in the drill code:
https://reviews.apache.org/r/44043/
Can someone please review it?

Thanks,
Smidth