selective rocotorun

[samtrahan]

In order to support issue #18, we need the ability to tell rocotorun to run only part of the workflow. Specifically, it should have the same arguments as discussed in #17: the -t, -m, -c, and -a arguments as are used in rocotoboot, rocotocomplete, and rocotorewind. The internal implementation of this is actually quite straightforward; it just requires rearranging the task and cycle selection code, and adding a method in the WorkflowEngine to check whether a cycle and task are selected. Before the various WorkflowEngine methods submit tasks or start cycles, they check if the task and cycle are selected. Half of that work has already been done to support issue #17.

Work on this feature will begin today.

[samtrahan]

Duplicate of #17