Update travis build image to be chapel-lang.
Make tests python 2.6 compatible.

* Update test case module to work with subprocess module and python 2.6 (remove
  unicode_literals)
* Update tuples test to deal with floating point precision error that
  manifested with 2.6.
Merge pull request #1 from thomasvandoren/py26-compat

Make tests python 2.6 compatible.

* Update test case module to work with subprocess module and python 2.6 (remove
  unicode_literals)
* Update tuples test to deal with floating point precision error that
  manifested with 2.6.

r: @lydia-duncan