Enable BMC patching from the /usr/local path

This commit enables patches from the /usr/local path by replacing
absolute paths to /usr/sbin or /usr/bin in every service file with
"/usr/bin/env ". Additionally, SyslogIdentifier is added to each
file to ensure that journal entries are still distinct.

In two cases, service files also had to change due to references
to ${{PATH}}, which doesn't work with /usr/bin/env. These
references - and the corresponding definitions - were changed to
${{DEVPATH}}.

Resolves openbmc/openbmc#2149

Change-Id: I12c5c6e5101eef6820b985a563313836250ff2c7
Signed-off-by: Michael Tritz <mtritz@us.ibm.com>
diff --git a/common/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service b/common/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
index 02d593c..5d58709 100644
--- a/common/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
+++ b/common/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
@@ -4,7 +4,8 @@
 After=network.target
 
 [Service]
-ExecStart={sbindir}/slpd
+ExecStart=/usr/bin/env slpd
+SyslogIdentifier=slpd
 Restart=always
 
 [Install]