invoker command line support for dynamicId assignment

[dgrove-oss]

As discussed in the review of #2689, for Mesos it is not feasible to use environment variables to communicate the unique invoker names. For Mesos, we need to also support command-line flags style of specifying arguments. For example:
--name <some_name> --id <proposed_id>
For Kubernetes, we really would prefer environment variables.

So, the plan is to support both options. Add flags-style command line argument processing to the invoker and read the environment if explicit command lines are not provided.

[dgrove-oss]

Please label as enhancement and assign to me. I plan to work on this next week.

[dgrove-oss]

Implemented in PR #2939

[dgrove-oss]

PR merged