upgrade.log now owned by vdsm:kvm

Bug:
If the admin installs VDSM, but before VDSM's first run
manually calls vdsm-tool (As root) then /var/log/vdsm/upgrade.log
is created with root:root file privileges. However, if vdsm-tool
is not manually used before VDSM's first run then upgrades
will be ran under the vdsm user, so /var/log/vdsm/upgrade.log
will be created with vdsm:kvm privileges.

Fix:
* Create upgrade.log in only one place by separating it out to
  a new logging conf file
* Make sure that upgrade.log is owned by vdsm:kvm when it is created

Change-Id: Ie2fb887fa6d43f2b35f4a07927026baa746e7a41
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22349
Reviewed-by: Dan Kenigsberg <danken@redhat.com>