Set custom cpu_model for live_migrate

live migrating a instance requires the same (or at least very similar)
cpu models on both instances. Since we don't always have this set a
custom one that is safe to use (tested by trial and error).

Switch to 32bit cirros to work with the custom CPU type.
32bit Cirros image caching added in
I47da72a0e9da3689cb085bb43ac6536094445112

Note: need to pick the least common denominator between all of our test
nodes.

Note: using devstack post-config options which are set via local.conf

Change-Id: I64a51ffb937cfa8398cc765836fd903cb6b1ff42

devstack-vm-gate.sh

@@ -336,6 +336,7 @@ EOF
     fi
 
     if [[ "$DEVSTACK_GATE_TOPOLOGY" != "aio" ]]; then
+        echo "CIRROS_ARCH=i386" >> "$localrc_file"
         echo "NOVA_ALLOW_MOVE_TO_SAME_HOST=False" >> "$localrc_file"
         local primary_node=`cat /etc/nodepool/primary_node_private`
         echo "SERVICE_HOST=$primary_node" >>"$localrc_file"
@@ -437,6 +438,7 @@ else
 
     if [[ "$DEVSTACK_GATE_TOPOLOGY" != "aio" ]]; then
         set -x  # for now enabling debug and do not turn it off
+        echo -e "[[post-config|\$NOVA_CONF]]\n[libvirt]\ncpu_mode=custom\ncpu_model=pentiumpro" >> local.conf
         setup_localrc "new" "$OVERRIDE_ZUUL_BRANCH" "sub_localrc" "sub"
         sudo mkdir -p $BASE/new/.ssh
         sudo cp /etc/nodepool/id_rsa.pub $BASE/new/.ssh/authorized_keys
@@ -536,6 +538,7 @@ EOF
             sudo cp sub_localrc tmp_sub_localrc
             echo "HOST_IP=$NODE" | sudo tee --append tmp_sub_localrc > /dev/null
             remote_copy_file tmp_sub_localrc $NODE:$BASE/new/devstack/localrc
+            remote_copy_file local.conf $NODE:$BASE/new/devstack/local.conf
             remote_command $NODE sudo chown -R stack:stack $BASE
             echo "Running devstack on $NODE"
             remote_command $NODE "cd $BASE/new/devstack; source $WORKSPACE/test_env.sh; export -n PROJECTS; sudo -H -u stack stdbuf -oL -eL ./stack.sh > /dev/null"