Add [GS]etContainer{Run}DirectoryFile
Add [GS]etContainer{Run}DirectoryFile

Add helper functions for stowing and reading back data in the
container's directory and run directory, so that the caller can do
things like stowing files named "config.json" in the right place with
fewer lines of code.

Signed-off-by: Nalin Dahyabhai <f562fcb2a0b898bf0be1afc867ea92325d8f825f@redhat.com>

containers/storage,containers/storage,containers/storage,rhatdan/storage,rhatdan/storage,rhatdan/storage