fix #113: get the update-ipxe target working

[realtime-neil]

Delete the vendored source under thirds_party/ipxe and replace it with a submodule reference to https://github.com/ipxe/ipxe.git at commit 8f1514a00450119b04b08642c55aa674bdf5a4ef a.k.a. tag v1.20.1 a.k.a. the latest release as of this writing.

Edit Makefile to change the rule body of the update-ipxe target:

• Discover the full path of pixiecore/boot.ipxe; i.e., the EMBED script given to the ipxe build.

• Use $(MAKE) -C instead of subshelled cd.

• Leave the four built ipxe binaries where they are built.

• Change the go-bindata to operate on the four files (instead of the directory that contains them), write to out/ipxe/bindata.go (instead of third_party/ipxe/ipxe-bin.go), and lose the -prefix.

Edit cmd/pixiecore/main.go use the new ipxe import path and reference the binaries by the longer, un-prefixed path keys.

Add out/ipxe/bindata.go, the thing generated by go-bindata. Yeah, we shouldn't source-control that which we can generate, but...

• ipxe builds are not reproducible (yet)

• building those four binaries takes a appreciable amount of time

• we can avoid a build-time dependency on go-bindata

Remove third_party/Makefile because it looks like dead code. At any rate, it seems this patch obviates everything it may have done.

[danderson]

Wow, github does not deal well with a change that alters 1700 files :D

Thanks for fixing this up!

[realtime-neil]

@danderson no problem, happy to help!

[realtime-neil]

@danderson I screwed up --- I don't think the ipxe artifacts in out/ipxe/bindata.go actually contain the embedded script. I may have assumed too much about how the ipxe makefile works.

Working on a fix

[realtime-neil]

@danderson I got it: https://github.com/ipxe/ipxe/pull/115