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/package/czechlight-cfg-fs/cfg-restore-sysrepo.service b/package/czechlight-cfg-fs/cfg-restore-sysrepo.service
index c990d56..9fe0c8a 100644
--- a/package/czechlight-cfg-fs/cfg-restore-sysrepo.service
+++ b/package/czechlight-cfg-fs/cfg-restore-sysrepo.service
@@ -7,6 +7,7 @@
 
 [Service]
 Type=oneshot
+RemainAfterExit=yes
 ExecStart=/bin/sysrepocfg -d startup -f json --import=/cfg/sysrepo/startup.json
 ExecStart=/bin/sysrepocfg -C startup