src/mount: use g_auto helpers for automatic cleanup
src/mount: use g_auto helpers for automatic cleanup

Also stop leaking GSubprocess in r_mount_full() and r_umount()

Signed-off-by: Philipp Zabel <db7328bbf81a38b011e8d0f5302fd54c788d0608@pengutronix.de>

jluebbe/rauc,rauc/rauc,ejoerns/rauc,ejoerns/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc,rauc/rauc,jluebbe/rauc