Bumped version of linuxkit

[micahhausler]

Description

Linuxkit has removed the -disable-content-trust flag

• removed deprecated linuxkit flag from Makefile
• Added clean Make target
• Added build dirs to gitignore
• Fixed broken CI from Fixes path to correct image #48

Why is this needed

I couldn't get the previously used version of linuxkit to build.

How Has This Been Tested?

I built a hook image locally and booted a Tink worker with the latest version of linuxkit

How are existing users impacted? What migration steps/scripts do we need?

Users can use and build a with a newer version of linuxkit

Checklist:

I have:

• updated the documentation and/or roadmap (if required): N/A
• added unit or e2e tests: N/A
• provided instructions on how to upgrade: N/A

[thebsdbox]

@micahhausler Looks like the sha256 needs updating to -> 1hx5k0l9gniz9aj9li8dkiniqs77pyfcl979y75yqm3mynrdz9ca

[micahhausler]

Not sure what the failure is. It looks like its missing an image?

linuxkit build -docker -pull -format kernel+initrd -name hook-x86_64 -dir out hook-ci.yaml
Extract kernel image: localhost:5000/tinkerbell/hook-kernel:5.10.11
Image localhost:5000/tinkerbell/hook-kernel:5.10.11 not found in local cache, pulling
time="2021-06-18T15:15:19Z" level=fatal msg="Failed to extract kernel image and tarball: Could not pull image localhost:5000/tinkerbell/hook-kernel:5.10.11: error getting manifest for trusted image localhost:5000/tinkerbell/hook-kernel:5.10.11: GET http://localhost:5000/v2/tinkerbell/hook-kernel/manifests/5.10.11: MANIFEST_UNKNOWN: manifest unknown; map[Tag:5.10.11]"

[micahhausler]

So GH runs a merge before running CI, which was confusing the situation.

@thebsdbox I think #48 broke CI, but it should be doing the right thing now