docker ulimit and pid default values for user container are hardcoded

This values should be expose and be configurable not hard coded.
Related to #3229
https://github.com/apache/incubator-openwhisk/blob/master/core/invoker/src/main/scala/whisk/core/invoker/InvokerReactive.scala#L82

Read core/invoker/src/main/scala/whisk/core/invoker/InvokerReactive.scala around line 82, then review related issue #3229. Identify where the Docker ulimit and PID defaults are hardcoded and how user-container settings are configured elsewhere. Done means both values are externally configurable rather than fixed defaults.

Written by the indexing model from the issue text.