switchroot: Move late /run/ostree-booted creation to ostree-system-generator
When ostree-prepare-root is pid 1, ostree-prepare-boot defers creation of
/run/ostree-booted, which happens in ostree-remount, but that's too late
if we need ostree-system-generator to bind /var. Add the creation of the
/run/ostree-booted marker to ostree-system-generator based on the
existence of the ostree= kernel command line argument (which matches the
condition that ostree-remount uses).
Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Closes: #1675
Approved by: cgwalters