Asserting CHPL_COMM=none for X* whitebox testing

[reviewed by diten]

With Lydia's commit to make GASNet the default for Cray machines,
our whitebox testing needed an update to assert CHPL_COMM=none,
both for consistency with what we're doing now, and because (I
believe) the binaries wouldn't work on a whitebox anyway.



git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@21913 3a8e244f-b0f2-452b-bcba-4c88e055c3ca