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/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service b/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
index a4b0902..a9644a7 100644
--- a/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
+++ b/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
@@ -4,4 +4,5 @@
 [Service]
 Restart=no
 EnvironmentFile={envfiledir}/obmc/gpio/%I
-ExecStart={sbindir}/phosphor-gpio-monitor --path=${{PATH}} --key=${{KEY}} --polarity=${{POLARITY}} --target=${{TARGET}}
+ExecStart=/usr/bin/env phosphor-gpio-monitor --path=${{DEVPATH}} --key=${{KEY}} --polarity=${{POLARITY}} --target=${{TARGET}}
+SyslogIdentifier=phosphor-gpio-monitor