Refactor and reorganize riak_test_escript module

[kellymclaughlin]

Refactor the riak_test_escript module to improve code clarity and
organization. This includes renaming functions to be more reflective
of their purpose and breaking large functions into smaller
functions.

Also add the ability to specify a comma-separated list of
tests with the -t option.

[kellymclaughlin]

This is part of the #667 refactoring effort

[bowrocker]

This is great!

janderson::Jons-MacBook-Pro { ~/sandbox/riak_test_decouple/riak_test }->  ./riak_test -c rtee -t bucket_types,http_bucket_types,verify_build_cluster
Tests to run: [{verify_build_cluster,
                   [{id,-1},
                    {platform,<<"local">>},
                    {version,<<"riak_ee-2.0.0beta6-11-g5a161cf-develop">>},
                    {project,<<"riak_ee">>}]},
               {http_bucket_types,
                   [{id,-1},
                    {platform,<<"local">>},
                    {version,<<"riak_ee-2.0.0beta6-11-g5a161cf-develop">>},
                    {project,<<"riak_ee">>}]},
               {bucket_types,
                   [{id,-1},
                    {platform,<<"local">>},
                    {version,<<"riak_ee-2.0.0beta6-11-g5a161cf-develop">>},
                    {project,<<"riak_ee">>}]}]
----SNIP----
Test Results:
verify_build_cluster-bitcask: pass
http_bucket_types-bitcask   : pass
bucket_types-bitcask        : pass
---------------------------------------------
0 Tests Failed
3 Tests Passed
That's 100.0% for those keeping score

👍