Add tests for list outputs with optionals

[rhpvorderman]

Motivation

I found a bug when running this task: https://github.com/biowdl/tasks/blob/a980f109ae7e3d13e8bc26e27b4411cc94f0eeb3/picard.wdl#L139

The task has lots and lots of outputs. Some of which are optional. Therefore an allOutputs variable is created on a list of all outputs using select_all. Miniwdl crashes on this latter list variable. I have created a reproducing test case.

Approach

TODO: Actually fix the bug

[mlin]

Included in 4def324 thanks#

[rhpvorderman]

Thanks! I will continue testing miniwdl with biowdl and report what shows up. (And also report if nothing shows up). Preliminary data shows that we can shorten some of the tests that take 10 minutes with cromwell to just 2 minutes with miniwdl. I am quite excited about this.