Add some tuple parameters to test model

[WardBrian]

Submission Checklist

• [x] Run unit tests: ./runTests.py src/test/unit
• [x] Run cpplint: make cpplint
• [x] Declare copyright holder and open-source license: see below

Summary

Adds more parameters to the test module used in the unconstrain_array round-trip test: https://github.com/stan-dev/stan/blob/develop/src/test/unit/model/array_functions_roundtrip_test.cpp

This was tested during the development of tuples, but adding it to these tests should help spot regressions in the future.

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):

Simons Foundation

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)