spec: fix libvirt dependency for fedora and RHEL7

In commit 395c77c90c0bc we bumped the libvirt requirement
to 1.2.3, which is found on RHEL 7.1 snapshots and
in fedora 20 with virt-preview repos.

This rules out RHEL 7.0 and Centos 7.0, thus a quite
relevant part of users.

This patch downgrades the libvirt requirements to 1.1.1
both for rpm and deb based systems with the following
rationale:

* commit 395c77c90c0bc already has soft dependency and
  could handle gracefully an old libvirt.
* CentOS/RHEL 7.0 provides libvirt 1.1.1, so it is fine
  out of the box. [1]
* Fedora 19 has libvirt 1.0.5.8 by default, but the
  virt-preview repo which already recommend provides
  libvirt 1.1.3 [2]
* Fedora 20 has libvirt 1.1.3 by default and libvirt 1.2.9
  through the virt-preview repo. [3]

References:
[1] http://mirror.centos.org/centos/7/os/x86_64/Packages/
[2] https://repos.fedorapeople.org/repos/crobinso/virt-preview/fedora-19/
[3] https://repos.fedorapeople.org/repos/crobinso/virt-preview/fedora-20/

Change-Id: Ia9c557281766d335b4c627aed4570a9099005ac0
Bug-Url: https://bugzilla.redhat.com/??????
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34340
Reviewed-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>