Add tests for #212

So far I can't reproduce what @syohex said on
https://github.com/peco/peco/issues/212#issuecomment-66556379 :(
Test for --layout being empty

This is the actual cause for #212
Make sure we have the correct default values for layoutType

1. the peco command's --layout should have a default value
2. NewCtx(...) should not set the value of layoutType if the value is ""

fixes #212
Merge pull request #214 from peco/topic/issue-212

Topic/issue 212