lib/sysroot: Port a few functions to new style
lib/sysroot: Port a few functions to new style

Not sure why we didn't do this earlier. Just noticed them when looking at the
code for a different reason.

Closes: #1085
Approved by: jlebon

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