Remove some unnecessary intermediate variables.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>
Allow mkdir_p to accept the empty string.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>
Generalized version for adding extra folders to installation media

This patch allows the user to add extra folders to the
installation media. This is useful for windows use case, as it
allows to put the $OEM$ folder for customization. In other
environments, it can be used for placing extra content that needs
to be loaded from the installation media.
Add ftp transfers to supported extra ISO types
Add http support to the extraiso mechanism

Signed-off-by: Chris Lalancette <clalancette@gmail.com>