build: Write out stub passwd/group files so that getpwuid() works
build: Write out stub passwd/group files so that getpwuid() works

Some bits of (broken) software attempt to look up the build user.  For
example, ibus presently runs dbus-launch to then invoke gsettings so
it can generate a text file.  dbus errors out when it's not able to
find its uid, of course.

We can help these bits of software along by generating an /etc/passwd
in the build environment that "works".

chergert/gnome-continuous,GNOME/gnome-ostree,vrutkovs/vrutkovs.github.io,vrutkovs/vrutkovs.github.io,djdeath/gnome-ostree,djdeath/gnome-ostree,vrutkovs/vrutkovs.github.io,djdeath/gnome-ostree,GNOME/gnome-ostree,GNOME/gnome-ostree,chergert/gnome-continuous,chergert/gnome-continuous