* Rework cache key generation a bit.
Cache keys are now based on the previous commands, rather than the previous state
of the filesystem.
* Refactor command interface a bit, only cache the context for commands that use it.
* 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
* Vendor changes for go-containerregistry switch.
* Manual changes for go-containerregistry switch.
The biggest change is refactoring the tarball unpacking.
* Pull more of container-diff out.
* More vendor removals.
* More unit tests.
Don McCasland
dlorenc
Nick Kubala
Jon Johnson
Sharif Elgamal
Priya Wadhwa
Matt Rickard