A first cut at generating solo.rb from knife.rb

thoughts @tmatilai?
Automatically expanding relative paths in solo.rb
Manifest update
WIP: Using knife.rb to configure and generate solo.rb
Include submodules in manifest
Update manifest
Fix test stub
Use explicit home dir in provisioning path.

Fixes #212
Will probably break windows nodes where shell is cmd.exe-based
Don't nest kitchen directories on the node
Include data bag key in default knife.rb

Just don't try to transfer it if it's missing.
Don't clobber existing knife.rb
Avoid checking data bag secret if option isn't set
Pull out config object

Since we rely on knife.rb and controlling the resulting paths, this config object seemed like more overhead than we need.
Fix path to search cookbook submodule
Manifest fix
Sort development dependencies in gemspec
Remove hard dependency on Librarian-Chef

Only try to use the librarian gem if the Cheffile is found (and
`--no-librarian` is not specified). Complain to the user with
instructions if the gem is not found.

Also add a debug message is the Cheffile is not found.
Add unit tests for librarian gem detection
Try to load Librarian dependencies only if really needed
Lock down librarian dev dependency to v0.0.x

librarian v0.1.0 will not include librarian-chef any more,
as it will be extracted to own gem.