Use systemd substitutions

Make use of the new substitution feature in the Phosphor
systemd bitbake class.

Change-Id: I2db85347809ef557a53e92af3ffcf17c8003b3ce
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/common/recipes-phosphor/console/obmc-console/obmc-console-ssh@.service b/common/recipes-phosphor/console/obmc-console/obmc-console-ssh@.service
index 74d5a7a..c3fcc03 100644
--- a/common/recipes-phosphor/console/obmc-console/obmc-console-ssh@.service
+++ b/common/recipes-phosphor/console/obmc-console/obmc-console-ssh@.service
@@ -4,8 +4,8 @@
 
 [Service]
 Environment="DROPBEAR_RSAKEY_DIR=/etc/dropbear"
-EnvironmentFile=-/etc/default/dropbear
-ExecStart=-@SBINDIR@/dropbear -i -r ${DROPBEAR_RSAKEY_DIR}/dropbear_rsa_host_key -c @BINDIR@/obmc-console-client $DROPBEAR_EXTRA_ARGS
-ExecReload=@BASE_BINDIR@/kill -HUP $MAINPID
+EnvironmentFile={envfiledir}/dropbear
+ExecStart=-{sbindir}/dropbear -i -r ${DROPBEAR_RSAKEY_DIR}/dropbear_rsa_host_key -c {bindir}/obmc-console-client $DROPBEAR_EXTRA_ARGS
+ExecReload={base_bindir}/kill -HUP $MAINPID
 StandardInput=socket
 KillMode=process