Implement Development mode for ISO build

Currently, our development environment lacks of many features we would like to have in our development or Quality Assurance process. Firstly, fuel needs Virtual Box Additions/Vmware Guest additions. It requires to add Virtual Box Guest Addition ISO to our repo, it requires modification of cobbler to run special snippet to run snippet and install required Guest Additions.

Another sample is some special tools such as atop, ltrace, strace, tcpdump ... that helps with debugging process.

As a solution we may introduce DEV environment variable as a special task for make that adds all necessary guest addition ISOs to repos, installs some packages during OS provisioning ...