Hello, In my OpenStack cluster(newton) after the OS update(ubuntu 16.04) of compute nodes it is not possible to create new VM's. When I create a new VM it is showing in horizon as active and IP is also shown as allocated to the VM in the horizon. But ssh into the VM is not possible. Then I check the console log of the VMs and I found error related to root disk as below

 Gave up waiting for root device.  Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT!  LABEL=cloudimg-rootfs does not exist.  Dropping to a shell!


BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) [6n[  963.757213] random: nonblocking pool is initialized

After Inspecting libvirt in compute nodes I found all my newly created VM's are using sda and scsi and all of them have the above same error. All the VM's which I created before the update is working fine and is using vda and virtio. Then I checked the libvirt instance.xml file and I found libvirt is not allocating CPU to the VM's and it always using sda and scsi. I think this happened due to the OS update. How can I solve this issue?? any help is really appreciated. one of the instance.xml is as below

<domain type='kvm'>
  <name>instance-00000081</name>
  <uuid>d7c2feae-ce57-4492-b892-35b86d1559f6</uuid>
  <metadata>
    <nova:instance xmlns:nova="http://openstack.org/xmlns/libvirt/nova/1.0">
      <nova:package version="14.0.10"/>
      <nova:name>testingimage</nova:name>
      <nova:creationTime>2018-02-13 13:47:56</nova:creationTime>
      <nova:flavor name="m1.small">
        <nova:memory>1024</nova:memory>
        <nova:disk>10</nova:disk>
        <nova:swap>0</nova:swap>
        <nova:ephemeral>0</nova:ephemeral>
        <nova:vcpus>1</nova:vcpus>
      </nova:flavor>
      <nova:owner>
        <nova:user uuid="b378a2ff41af45bc8e458a2f17c30c3f">vmsec</nova:user>
        <nova:project uuid="7814cec0fc1943b6b08a1a052ffeb4f7">vmsec</nova:project>
      </nova:owner>
      <nova:root type="image" uuid="790b87d7-e345-47a8-9d5e-f7bcc6f7202b"/>
    </nova:instance>
  </metadata>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <cputune>
    <shares>1024</shares>
  </cputune>
  <sysinfo type='smbios'>
    <system>
      <entry name='manufacturer'>OpenStack Foundation</entry>
      <entry name='product'>OpenStack Nova</entry>
      <entry name='version'>14.0.10</entry>
      <entry name='serial'>5b8fe22f-532c-4114-b52a-905b91050f9b</entry>
      <entry name='uuid'>d7c2feae-ce57-4492-b892-35b86d1559f6</entry>
      <entry name='family'>Virtual Machine</entry>
    </system>
  </sysinfo>
  <os>
    <type arch='x86_64' machine='pc-i440fx-xenial'>hvm</type>
    <boot dev='hd'/>
    <smbios mode='sysinfo'/>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-model'>
    <model fallback='allow'/>
    <topology sockets='1' cores='1' threads='1'/>
  </cpu>
  <clock offset='utc'>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/kvm-spice</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/var ...