The fdisk version in Ubuntu trusty (provided by travis-ci) is different enough
from the one shipped with Debian Jessie to require few careful changes.
With this commit disk-create.sh should work on both version in the same way.
If not defined, SYSLINUXMBR is /usr/lib/syslinux/mbr/mbr.bin as in Debian GNU/Linux.
However, on travis-ci configuration, SYSLINUXMBR will be as expected in Ubuntu Trusty
/usr/lib/syslinux/mbr.bin
This should catch bugs introduced in the disk image generation, in hjfs
and in ahci driver. Also, the checks are run with a single core virtual
machine so that some kind of bugs I might introduce in the scheduler
could break the build.
