fix(build_library): make the usr link relative

Fix the problem of: "pecified switch root path %s does not seem to be an
OS tree. /etc/os-release is missing" because dracut doesn't have an
/usr/share/coreos/os-release file.
fix(build_library): use ln -sf instead of if

we don't need an if statement when we can force.
fix(build_library): put lsb-release in usr too
fix(build_library): mkdir /usr/share/coreos in the right order

This is important otherwise things fail to create files because the
directoreis don't exist.
Merge pull request #191 from philips/relative-link

Fixup all of the symlinks in set_lsb_release
fix(build_library): use http until we get certs on roller
Merge pull request #192 from philips/no-https-on-roller-yet

fix(build_library): use http until we get certs on roller
fix(set_lsb_release): Bear Creek Manor
Merge pull request #194 from marineam/name

fix(set_lsb_release): Bear Creek Manor
feat(vm_image_util): Add qemu_no_kexec image type

This makes it easy to test booting without kexec on qemu/kvm similar to
how images are booted on Xen.
cleanup(set_lsb_release): Rework release config setup

- Remove custom COREOS_* attributes from /etc/lsb-release
- Move dev image logic to dev_image_util
  For extra fun fix detection of local host URL for devserver.
- Remove weirdly verbose "DESCRIPTION" format.
- Add COREOS_RELEASE_BOARD back to /usr/share/coreos/release
  This is mostly just so update_engine and gmerge report the correct
  board name to devserver, informative-only on prod images.
- Remove version info from /etc/gentoo-release
- Switch from 'track' to 'group' terminology.
fix(vagrant): pad vagrant mac to six characters
Merge pull request #198 from bcwaldon/virtualbox-mac

fix(vagrant): pad vagrant mac to six characters
fix(build_image): Switch to SYSLINUX for our EFI bootloader.

Now with SYSLINUX 6 we can use the same bootloader on EFI and BIOS
systems. This replaces our previous reliance on building default kernel
options into the kernel image itself.
Merge pull request #197 from marineam/release-files

cleanup(set_lsb_release): Rework release config setup
Merge pull request #199 from marineam/syslinux

fix(build_image): Switch to SYSLINUX for our EFI bootloader.
fix(oem/ami): Add support for building release AMIs for amd64-usr
fix(oem/ami): Explicitly start etcd and fleet.
Merge pull request #200 from marineam/ami

fix(oem/ami): Add support for building release AMIs for amd64-usr
fix(make_chroot): Simplify chroot user creation.

The commands useradd/usermod will silently skip adding users to
secondary groups that are not in /etc/group. The idea being that the
tools should not create groups that conflict with existing LDAP/NIS
groups but why trying to do so isn't a fatal error I don't know.

Overall the code is rather complicated and tries to modify instead of
add when possible to allow running the SDK as the 'core' user. To keep
things simple gut this code, make the 'core' user special, and add
secondary groups via the 'gpasswd' command so that errors are reported
instead of silently ignored.

One functional change: the default groups have changed to kvm and
portage. The old list excluded kvm and included lots of extra cruft.