packaging: update httpd conf on engine-upgrade

If /etc/httpd/conf.d/ovirt-engine.conf exists,
the httpd configuration will be updated creating:
- /etc/httpd/conf.d/proxy_ovirt-engine.conf
- /etc/httpd/conf.d/ovirt-engine-root-redirect.conf

It will configure mod_deflate also on upgrade and not only
on install.

Change-Id: I73175ef2acc9cf88261eb7df4f17602085151b1c
Bug-Url: https://bugzilla.redhat.com/948783
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>