systemd: ship emergency.service which triggers a reboot

This reboots the system instead of starting a shell on boot problems.
Because the slot will only be marked as sucessfully booted as the last
step in a normal boot, repeated emergency boots will cause a fallback at
the boot chooser level to the other slot.

Testing this is possible by passing 'emergency' via the kernel command
line.

recipes-apps/tasks/task-sysmocom-tools.bb

@@ -3,7 +3,7 @@ LICENSE = "MIT"
 LIC_FILES_CHKSUM = " \
                     file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
 ALLOW_EMPTY_${PN} = "1"
-PR = "r9"
+PR = "r10"
 
 RDEPENDS_${PN} = "\
     lmsensors-scripts \
@@ -16,4 +16,5 @@ RDEPENDS_${PN} = "\
     ca-cacert-rootcert \
     sysmocom-backup \
     sysmocom-backup-default \
+    sysmocom-systemd \
     "

recipes-config/sysmocom-systemd/files/emergency.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=Emergency Reboot
+DefaultDependencies=no
+Conflicts=shutdown.target
+Before=shutdown.target
+
+[Service]
+ExecStart=/bin/systemctl --force reboot
+Type=oneshot

recipes-config/sysmocom-systemd/sysmocom-systemd_1.0.bb

@@ -0,0 +1,14 @@
+DESCRIPTION = "sysmocom systemd customization"
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
+
+SRC_URI = " \
+	file://emergency.service \
+"
+
+do_install() {
+	install -d ${D}${sysconfdir}/systemd/system
+	install -m 0644 ${WORKDIR}/emergency.service ${D}${sysconfdir}/systemd/system
+}
+
+CONFFILES_${PN} += "${sysconfdir}/systemd/system/emergency.service"