Move Go() promise-like func from utils to pkg/promise

This is the first of two steps to break the archive package's dependence
on utils so that archive may be moved into pkg.  Also, the `Go()`
function is small, concise, and not specific to the docker internals, so
it is a good candidate for pkg.

Signed-off-by: Rafe Colton <rafael.colton@gmail.com>
Move Matches() file path matching function into pkg/fileutils

This is the second of two steps to break the archive package's
dependence on utils so that archive may be moved into pkg. `Matches()`
is also a good candidate pkg in that it is small, concise, and not
specific to docker internals

Signed-off-by: Rafe Colton <rafael.colton@gmail.com>
Move archive package into pkg/archive

Now that the archive package does not depend on any docker-specific
packages, only those in pkg and vendor, it can be safely moved into pkg.

Signed-off-by: Rafe Colton <rafael.colton@gmail.com>