* added switch to extract different sources as build context
* first rough implementation of aws s3
* added buildcontext package and interface
* added GetBuildContext func to buildcontext.go
added fallback to gcs
renamed GC struct to GCS
* improved the default behavior of build context retrieval
* renamed gc:// to gs:// in order to follow common standards
* renamed struct File to Dir and some cleanup work
* moved context.tar suffix to the buildcontext processors where it is needed
* added buildcontext retrieval as struct variable
added fallback if prefix in bucket specifier is present
* cleanup if structures
* added prefix to s3
* WIP
* Fixed build context bugs
* refactored build context
* adding metadata tests back to integration tests and fixing resulting bugs
* fix onbuild and default env
* removing old test files
* adding the ArgsEscaped boolean on CMD commands
* fix onbuild test
* ignore failing test until container-diff is fixed
* code comments
* adding todo to remove uncomment failing test
peter-evans
Priya Wadhwa
Christian Jantz
Sharif Elgamal