How about we make this file name specification part of the riak_test configuration file and have a default of "hosts" or maybe even a less generic default name? Something like an `rtssh_hosts_file` entry in the `.riak_test.config` overrides the default. Seems like a nice balance by making it easy enough to swap between host files for different test setups while not polluting the primary configuration file by putting the host information directly into `.riak_test.config`.