Install knife solo databag gem.

In order to manipulate the encrypted databags easily,
install knife solo databag gem.

see: http://blog.kenjiskywalker.org/blog/2013/05/20/chef-databag/

This commit refs #199.
Specify the secret file for encryption.

see: http://blog.kenjiskywalker.org/blog/2013/05/20/chef-databag/

This commit fixes #199.
Merge branch 'id/199' into dev