travis: Add Travis CI config file

travis: Add Travis CI config file

There is a really convenient service for open source project from Travis
CI: They allow for free CI testing using their infrastructure.

GRUB has had issues with broken builds for various targets for a long time
already. The main reason is a lack of CI to just do smoke tests on whether
all targets still at least compile.

This patch adds a Travis config file which builds (almost) all currently
available targets.

On top of that, this Travis config also runs a small execution test on the
x86_64-efi target.

All of this config file can easily be extended further on. It probably
makes sense to do something similar to the u-boot test infrastructure
that communicates with the payload properly. Going forward, we also will
want to do more QEMU runtime checks for other targets.

Currently, with this config alone, I already see about half of the available
targets as broken. So it's definitely desperately needed :).

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>