Have .dockerignore support Dockerfile/.dockerignore

If .dockerignore mentions either then the client will send them to the
daemon but the daemon will erase them after the Dockerfile has been parsed
to simulate them never being sent in the first place.

Closes #8330

Signed-off-by: Doug Davis <dug@us.ibm.com>
Fair enough. @unclejack @vbatts what do you think about the current behavior of having `includes` not use filepath.Match but `excludes` yes ? Do we care about pkg/archive's API ? Is there a scenario where we would want to do filepath.Match-ing for `includes` in the future?