ostree: Add --view mode to `ostree summary`
ostree: Add --view mode to `ostree summary`

This allows a locally generated summary file to be viewed. It accepts
the same arguments as `ostree remote summary` (i.e. --raw).

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #826
Approved by: cgwalters

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree