Set RemainAfterExit for hostboot-settings service

The service hostboot-settings is required by multi-user.target and
thus will be started by default. In case multi-user.target is started
for multiple times, this service will be startd for multiple times as
well, and eventually get start-limit-hit failure.

This commit adds RemainAfterExit=true so the service will be treated as
started and thus will not be started for multiple times.

Resolves openbmc/openbmc#3544

Tested: Reboot Romulus BMC when the host is on, and verify the BMC gets
        READY state after reboot, and verify the service is only started
        once.

Change-Id: I0df2b37f2aee7b33068e95b9442da5e4f3cdd0a6
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/recipes-phosphor/host/hostboot-settings/hostboot-settings.service b/recipes-phosphor/host/hostboot-settings/hostboot-settings.service
index fbd4c06..9ce81d7 100644
--- a/recipes-phosphor/host/hostboot-settings/hostboot-settings.service
+++ b/recipes-phosphor/host/hostboot-settings/hostboot-settings.service
@@ -3,6 +3,7 @@
 
 [Service]
 Type=oneshot
+RemainAfterExit=true
 ExecStart=/usr/bin/hb_settings --uart vuart
 
 [Install]