Support Default Parameters for Sequences

Environment details:

IBM-Bluemix (US-South)

Steps to reproduce the issue:

 wsk action create test --sequence /whisk.system/combinators/trycatch  -p '$tryName' foo -p '$catchName' bar

Provide the expected results and outputs:

Looking at wsk action get test I can see that the parameters passed during the creation are ignored.

Digging into the code, I can see this snippet which looks like the culprit. https://github.com/openwhisk/openwhisk/blob/10c182b26427e61db23a4a829fa5739dd6387c5a/core/controller/src/main/scala/whisk/core/controller/Actions.scala#L354-L362

Additional information you deem important:

Being able to store default parameters for a sequence action provides a convenient way to define new actions from the combinator actions without having to pass in the parameters each time or bind them into a separate package for each instance.