phosphor-watchdog: don't enable watchdog on BMC reboot

There are applications we do not want to reenable after a BMC reboot and
the typical mechanism for that is a ConditionPathExists on a marker file
we create in /run.  This was missing for the Host watchdog enable
service, which caused the watchdog to be re-enabled even though the boot
process was complete.  Add the ConditionPathExists to prevent it from
becoming enabled.

Resolves openbmc/openbmc#1948.

Change-Id: Ibb64ee40d9b6313bc44205c751d130345be695ed
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meta-phosphor/common/recipes-phosphor/watchdog/phosphor-watchdog/obmc-enable-host-watchdog@.service b/meta-phosphor/common/recipes-phosphor/watchdog/phosphor-watchdog/obmc-enable-host-watchdog@.service
index 1fc88f3..a921fc3 100644
--- a/meta-phosphor/common/recipes-phosphor/watchdog/phosphor-watchdog/obmc-enable-host-watchdog@.service
+++ b/meta-phosphor/common/recipes-phosphor/watchdog/phosphor-watchdog/obmc-enable-host-watchdog@.service
@@ -5,6 +5,7 @@
 Wants=mapper-wait@-xyz-openbmc_project-watchdog-host%i.service
 After=mapper-wait@-xyz-openbmc_project-watchdog-host%i.service
 Conflicts=obmc-host-stop@%i.target
+ConditionPathExists=!/run/openbmc/host@%i-on
 
 [Service]
 Type=oneshot