Fix directory creation on running make with docker target
Fix directory creation on running make with docker target

On running "make docker" we have other targets
workflow then on "make iso", so for building target
$(ISOROOT)/openstack_version we must be sure that $(ISOROOT)
directory exists.

Closes-bug: #1457435
Change-Id: Ifa0ca2f81074d1be040cebb99f3632bcc7270dd9

AnselZhangGit/fuel-main,eayunstack/fuel-main,stackforge/fuel-main,SmartInfrastructures/fuel-main-dev,huntxu/fuel-main,teselkin/fuel-main,AnselZhangGit/fuel-main,huntxu/fuel-main,SergK/fuel-main,stackforge/fuel-main,eayunstack/fuel-main,stackforge/fuel-main,SmartInfrastructures/fuel-main-dev,SergK/fuel-main,SergK/fuel-main,AnselZhangGit/fuel-main,SmartInfrastructures/fuel-main-dev,AnselZhangGit/fuel-main,SmartInfrastructures/fuel-main-dev,eayunstack/fuel-main,teselkin/fuel-main,teselkin/fuel-main,huntxu/fuel-main,teselkin/fuel-main