Prettify the output of describe, making use of existing stuff.
Dat whitespace
Update output to print special text when a key or default is not set.
Add test for the escript and improved describe command.

* Slurped and modified the group leader code from riak_test.
* Added an assertion and some macros to help with the test.
Merge pull request #136 from basho/feature/sdc/better-describe

Better 'describe' command output, supersedes #134.