MDADM provider:  Don't pass chunk size for mirrors

Mirros don't use chunk size.  MDADM ignores it currently, but Chef
really shouldn't be passing it.  It's easy enough to avoid.
Fix test failures
Switch default mdadm tests to creat a raid 5 array and add a test to
make sure raid 1 devices dont pass chunksize
Merge branch 'CHEF-4465' into contributions