Guys ! i've recently installed Centos7 then packstack all in one , all services work fine , but i'm not able to launch an instance i always get this annoying error message

No valid host was found

the first error in /var/log/nova/nova-compute.log is :

 2016-08-07 10:57:49.836 18979 WARNING nova.virt.osinfo [req-5e66fd40-5776-40e3-8396-d1aae75edb41 09b70c56e97049bd9559e55d863be90c 9076e9553ad64346941c167696b54aba - - -] Cannot find OS information - Reason: (No configuration information found for operating system Empty)
2016-08-07 10:57:56.308 18979 ERROR nova.virt.libvirt.guest [req-5e66fd40-5776-40e3-8396-d1aae75edb41 09b70c56e97049bd9559e55d863be90c 9076e9553ad64346941c167696b54aba - - -] Error defining a domain with XML: <domain type="kvm">
  <uuid>2fde03ee-6f8f-4067-b277-901f93283100</uuid>
  <name>instance-0000000f</name>
  <memory>256000</memory>
  <vcpu>1</vcpu>
  <metadata>
    <nova:instance xmlns:nova="http://openstack.org/xmlns/libvirt/nova/1.0">
      <nova:package version="13.1.0-1.el7"/>
      <nova:name>llklk</nova:name>
      <nova:creationTime>2016-08-07 14:57:49</nova:creationTime>
      <nova:flavor name="j">
        <nova:memory>250</nova:memory>
        <nova:disk>1</nova:disk>
        <nova:swap>0</nova:swap>
        <nova:ephemeral>1</nova:ephemeral>
        <nova:vcpus>1</nova:vcpus>
      </nova:flavor>
      <nova:owner>
        <nova:user uuid="09b70c56e97049bd9559e55d863be90c">admin</nova:user>
        <nova:project uuid="9076e9553ad64346941c167696b54aba">admin</nova:project>
      </nova:owner>
      <nova:root type="image" uuid="bf0f1177-f27a-4635-9fcc-bfecbc7cea99"/>
    </nova:instance>
  </metadata>
  <sysinfo type="smbios">
    <system>
      <entry name="manufacturer">Fedora Project</entry>
      <entry name="product">OpenStack Nova</entry>
      <entry name="version">13.1.0-1.el7</entry>
      <entry name="serial">f0c0207f-a705-4e4e-9148-e443c12a821b</entry>
      <entry name="uuid">2fde03ee-6f8f-4067-b277-901f93283100</entry>
      <entry name="family">Virtual Machine</entry>
    </system>
  </sysinfo>
  <os>
    <type>hvm</type>
    <boot dev="hd"/>
    <smbios mode="sysinfo"/>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cputune>
    <shares>1024</shares>
  </cputune>
  <clock offset="utc">
    <timer name="pit" tickpolicy="delay"/>
    <timer name="rtc" tickpolicy="catchup"/>
    <timer name="hpet" present="no"/>
  </clock>
  <cpu mode="host-model" match="exact">
    <topology sockets="1" cores="1" threads="1"/>
  </cpu>
  <devices>
    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2" cache="none"/>
      <source file="/var/lib/nova/instances/2fde03ee-6f8f-4067-b277-901f93283100/disk"/>
      <target bus="virtio" dev="vda"/>
    </disk>
    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2" cache="none"/>
      <source file="/var/lib/nova/instances/2fde03ee-6f8f-4067-b277-901f93283100/disk.eph0"/>
      <target bus="virtio" dev="vdb"/>
    </disk>
    <interface type="bridge">
      <mac address="fa:16:3e:c9:10:d0"/>
      <model type="virtio"/>
      <source bridge="qbr9f64214e-67"/>
      <target dev="tap9f64214e-67"/>
    </interface>
    <serial type="file">
      <source path="/var/lib/nova/instances/2fde03ee-6f8f-4067-b277-901f93283100/console.log"/>
    </serial>
    <serial type="pty"/>
    <input type="tablet" bus="usb"/>
    <graphics type="vnc" autoport="yes" keymap="en-us" listen="0.0.0.0"/>
    <video>
      <model type="cirrus"/>
    </video>
    <memballoon model="virtio">
      <stats period="10"/>
    </memballoon>
  </devices>
</domain>

when i issue ip a command i get :

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp7s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
    link/ether 70:5a:0f:94:c4:92 brd ff:ff:ff:ff:ff:ff
3 ...