systemd: RemainAfterExit=yes for all Type=oneshot units

Many of these are intended to run as a one-time thingy. Some of them,
such as the YANG installation bits, have been failing since the recent
switch to storing sysrepo config as a JSON file (and the related change
of not preserving /etc/sysrepo/ directly).

One especially nasty scenario is a random failure in cla-sysrepo which
leads to an automatic restart, which triggers czechlight-install-yang,
which fails horribly. Yay.

Change-Id: I76664c5fb2b8eb62a12fd19a31fc606fa7c3723c
diff --git a/board/czechlight/beaglebone/overlay/usr/lib/systemd/system/save-machineid-to-uboot.service b/board/czechlight/beaglebone/overlay/usr/lib/systemd/system/save-machineid-to-uboot.service
index 892411b..4a74b83 100644
--- a/board/czechlight/beaglebone/overlay/usr/lib/systemd/system/save-machineid-to-uboot.service
+++ b/board/czechlight/beaglebone/overlay/usr/lib/systemd/system/save-machineid-to-uboot.service
@@ -3,4 +3,5 @@
 
 [Service]
 Type=oneshot
+RemainAfterExit=yes
 ExecStart=/bin/sh -c 'fw_printenv machineid &>/dev/null || fw_setenv machineid $(cat /etc/machine-id)'