Change Ironic bm flavor to use ephemeral partition

Adds use of the IRONIC_VM_EPHEMERAL_DISK variable to devstack
that will alter the flavor to specify an ephemeral partition
size. This change creates a 1 GB ephemeral partition, which
will be deducted from the overall disk size (IRONIC_VM_SPECS_DISK).

Change-Id: I37374d3fa8fd1b5cd194ac9659044031a3cad19e

devstack-vm-gate.sh

@@ -115,6 +115,7 @@ EOF
     if [ "$DEVSTACK_GATE_VIRT_DRIVER" == "ironic" ]; then
         echo "VIRT_DRIVER=ironic" >>localrc
         echo "IRONIC_BAREMETAL_BASIC_OPS=True" >>localrc
+        echo "IRONIC_VM_EPHEMERAL_DISK=1" >>localrc
         echo "DEFAULT_INSTANCE_TYPE=baremetal" >>localrc
     fi