Implement files REST API

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Add basic support for pushing/pulling files

Here we have basic support for pushing and pulling files from containers. We
don't support recursive stuff right now (although it shouldn't be hard to add).

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Grab files from /proc/<pid>/root for running contianers

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Better handle errors for missing files

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Merge pull request #117 from tych0/files-api

Files api