Lower stack size for callStackSize test

This test is intended to show that the runtime changes stack size based off of
CHPL_RT_CALL_STACK_SIZE. It used to set the value to a little over 12MB.
However on cygwin our default and max stack size are 2MB so this just lowers
the value set to a little under 1MB. It doesn't really matter what the value is
so long as it's different than the default, and it's lower than the max across
different configurations.
Merge pull request #811 from ronawho/update-callStackSize-for-cygwin

Lower stack size for callStackSize test

[ok'd by @bradcray]

This test is intended to show that the runtime changes stack size based off of
CHPL_RT_CALL_STACK_SIZE. It used to set the value to a little over 12MB.
However on cygwin our default and max stack size are 2MB so this just lowers
the value set to a little under 1MB. It doesn't really matter what the value is
so long as it's different than the default, and it's lower than the max across
different configurations.