move Berksfile#apply to Lockfile#apply
Add helper function for loading a Lockfile from a Berksfile
fix broken lockfile specs

promote Berksfile#ridley_connection to ::Berkshelf
fix broken apply feature
add check for lockfile existence when running apply
Merge pull request #933 from berkshelf/GH-933

berks apply is an action on a lockfile, not a berksfile