Switching valgrind testing to bash rather than csh

We've had strange valgrind failures for the past few weeks that
we can't explain.  This is a completely superstitious change from
csh-based testing to bash-based which shouldn't affect anything,
but in my initial testing seems to have quieted things down.



git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@22126 3a8e244f-b0f2-452b-bcba-4c88e055c3ca