fix(firmware): Revert change to GptNextKernelEntry made in e3ecb4d9.

We rely on the new cgpt next command which doesn't use this related code
in cgptlib. Since this change breaks existing unit tests but isn't
required we can roll it back. Ideally all this kernel partition code
should be more generic so any partition type can be used but that's a
big change that we don't need right now.
Revert "fix(firmware/include/gpt.h): Set signature to CoreOS"

This reverts commit fb1c0619bdd1d86da9a345077ea15913430335da.

A couple issues here, GPT_HEADER_SIGNATURE2 must be the same length as
the generic GPT_HEADER_SIGNATURE but this commit broke that assumption.
Also, all of our images use GPT_HEADER_SIGNATURE, "EFI PART". The
purpose of this value is to hide EFI partition tables from Windows to
support some hacky ChromeOS/Windows dual boot scheme. See b7b865cf

Just revert back to the upstream value, we don't need to touch it.
fix(tests): Switch to coreos-rootfs type for cgpt prioritize tests.

cgpt prioritize expects coreos-rootfs now, not kernel. Update test
script accordingly. Now 'make runtests' works!!
add(travis): Add config for running tests in Travis
Merge pull request #5 from marineam/tests

Fix tests, setup for Tavis