Set default volume_device_name = vdb
Set default volume_device_name = vdb

refstack_defcore is currently failing on all installers.
It will highlight the right value per installer.

A better way is to manage the device name by a new env var set by all
installers (it may depend on kdrive configurations)

JIRA: FUNCTEST-947
Change-Id: If1c12bc6798bc89136715bc78f2ac0b798e669e6
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

mywulin/functest,opnfv/functest,mywulin/functest,opnfv/functest