debian: Fix packaging issues for sysinv-agent

- Ensure that the sysinv-agent.service starts.
- Ensure that the preset are installed when the package is
  installed.
- Removed unused sysinv-agent.postinst.

Test Plan
PASS Build packaage
PASS Build and Install ISO
PASS Ensure that the sysinv-agent service is
     running.

Story: 2009101
Task: 44678

Signed-off-by: Chuck Short <charles.short@windriver.com>
Change-Id: I9de28984f237841537264d408a9f848e030ced82

sysinv/sysinv-agent/debian/deb_folder/rules

@@ -15,4 +15,4 @@ override_dh_installinit:
 	dh_installinit --only-scripts
 
 override_dh_installsystemd:
-	dh_installsystemd --name sysinv-agent
+	dh_installsystemd -psysinv-agent sysinv-agent.service

sysinv/sysinv-agent/debian/deb_folder/sysinv-agent.install

@@ -1,2 +1,3 @@
 etc/init.d/sysinv-agent
 etc/pmon.d/sysinv-agent.conf
+debian/systemd/00-sysinv-agent.preset etc/systemd/system-preset

sysinv/sysinv-agent/debian/deb_folder/sysinv-agent.postinst

@@ -1,4 +0,0 @@
-#!/bin/sh
-set -e
-
-#DEBHELPER#

sysinv/sysinv-agent/debian/deb_folder/systemd/00-sysinv-agent.preset

@@ -0,0 +1 @@
+enable sysinv-agent.service