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/meta-phosphor/common/recipes-phosphor/flash/obmc-mgr-download/org.openbmc.managers.Download.service b/meta-phosphor/common/recipes-phosphor/flash/obmc-mgr-download/org.openbmc.managers.Download.service
index e7bd28b..f3ff75d 100644
--- a/meta-phosphor/common/recipes-phosphor/flash/obmc-mgr-download/org.openbmc.managers.Download.service
+++ b/meta-phosphor/common/recipes-phosphor/flash/obmc-mgr-download/org.openbmc.managers.Download.service
@@ -3,7 +3,8 @@
 
 [Service]
 Restart=always
-ExecStart={sbindir}/download_manager.py
+ExecStart=/usr/bin/env download_manager.py
+SyslogIdentifier=download_manager.py
 Environment="PYTHONUNBUFFERED=1"
 Type=dbus
 BusName={BUSNAME}