Description of problem:
The instack disk size is hard coded to 30G in the instack-virt-setup script.
The disk size should have default size of 30G but should use env variable to allow other sizes.

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1. see the image create command in the script:
 disk-image-create \
        --image-size 30 \
        -a amd64 \
        $NODE_DIST instack-vm \
        -o $UNDERCLOUD_VM_NAME

2.
3.

Actual results:


Expected results:


Additional info: