Add dict2columns()

Add ShowOne.dict2columns() to handle the common process of displaying
a single dict as two columns of key and value.
Merge pull request #37 from dtroyer/make-columns

Add make_columns() to show.ShowOne
add tests for dict2columns

Change-Id: I42e9a9a74af9f5608e67e20f131f6a7155179037
move tests into cliff package

Change-Id: I1c1f20b51fdfb84b3ed657d26dccedfd23e780eb