[fuel_devops]VMs don't see the hdd with default HDD size(50GB)

[Egor Kotko]

Volume should not be created with size less than backing_store volume.

Steps to reproduce:
1.ENV_NAME="bla" IMAGE_PATH="/home/ykotko/FRESH-FUEL_MAIN/nextgen/packer-ubuntu-1604-server-new.qcow2" WORKSPACE=/tmp DEPLOY_SCRIPT="/home/ykotko/FRESH-FUEL_MAIN/nextgen/fuel-ccp-installer/utils/jenkins/kargo_deploy.sh" SUSPEND_ENV_ON_TEARDOWN=false py.test -vvv -s mcp_tests/system_tests/test_kargo_deployed

Actual result:
After creation VMs can not find HDD:
https://snag.gy/ikI8Kh.jpg
https://snag.gy/Wr3qCp.jpg

The same command works fine if change the NODE_VOLUME_SIZE: !os_env NODE_VOLUME_SIZE, 50 on 150
https://review.openstack.org/gitweb?p=openstack/fuel-ccp-tests.git;a=blob;f=mcp_tests/templates/default.yaml;h=836322bf407a9c4c39c276101cf225687ea2d86e;hb=HEAD (string 83)