phosphor-hwmon: Fix unit escaping

We aren't correctly escaping all of the specical characters based on the
systemd spec for unit name escaping. systemd provides a utility to do
this reliably, so use that instead of a custom implementation.

(From meta-phosphor rev: e1acbce6ac818e411cee8483c89ea6f7b0829162)

Change-Id: I239f396f92e6a6b94edcfe48084c41dcc292e1b7
Signed-off-by: William A. Kennington III <wak@google.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-phosphor/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh b/meta-phosphor/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
index 2f35865..2e346d0 100755
--- a/meta-phosphor/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
+++ b/meta-phosphor/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
@@ -17,7 +17,8 @@
     fi
 fi
 
+# Needed to re-do escaping used to avoid bitbake separator conflicts
 path="${path//:/--}"
-path="${path//-/\\x2d}"
-
-systemctl --no-block $action 'xyz.openbmc_project.Hwmon@'$path'.service'
+# Needed to escape prior to being used as a unit argument
+path="$(systemd-escape "$path")"
+systemctl --no-block "$action" "xyz.openbmc_project.Hwmon@$path.service"