UBUNTU: Skip ABI checks for Endless

For Endless, we're making patches to a fixed Ubuntu linux ABI and
checking that the ABI is unchanged is just unwanted mechanical work.
Skip checking the module and symbol lists in the default build.

Ideally we'd be checking dpkg-vendor to determine this is Endless, but
we still report Ubuntu there and probably don't want to change that
until we determine what other effects it has. Use lsb_release to
determine the distribution.

[endlessm/eos-shell#4334]
UBUNTU: Skip cloud-tools for Endless

We'll never use the cloud-tools (hyperv) on Endless, so building just
wastes resources.

[endlessm/eos-shell#4334]
UBUNTU: Don't build lowlatency kernel for Endless

We only ever use the generic kernel, so building the lowlatency kernel
just wastes resources. It would be nice if this was just a conditional
we could lump under Endless, but the kernel flavours are built from
these lists, so we have to edit them directly.

[endlessm/eos-shell#4334]
UBUNTU: Don't build udebs for Endless

Make a new conditional, do_udebs, that skips building udebs when set to
false. Set this to false for Endless and for AUTOBUILD as before. For
Endless, we have no need for udebs in a Debian installer.

[endlessm/eos-shell#4334]
UBUNTU: release 3.13.0-27.50endless11

[endlessm/eos-shell#4334]
UBUNTU: Start new release

Ignore: yes
Merge pull request #17 from endlessm/shell/4334

Speed up linux build