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/fans/phosphor-fan/phosphor-fan-control@.service b/common/recipes-phosphor/fans/phosphor-fan/phosphor-fan-control@.service
index 773e59e..2aef875 100644
--- a/common/recipes-phosphor/fans/phosphor-fan/phosphor-fan-control@.service
+++ b/common/recipes-phosphor/fans/phosphor-fan/phosphor-fan-control@.service
@@ -4,7 +4,8 @@
 
 [Service]
 Restart=on-failure
-ExecStart={sbindir}/phosphor-fan-control --control
+ExecStart=/usr/bin/env phosphor-fan-control --control
+SyslogIdentifier=phosphor-fan-control
 
 [Install]
 RequiredBy=obmc-fan-control-ready@%i.target