add every unique header to kernel headers mount

[michiboo]

#727

[ctalledo]

Hi @michiboo, apologies for the delay in reviewing and thanks very much for your contribution.

I looked at the propose change, and I think it's a band-aid in the test container that in a way hides a deeper bug in sysbox-mgr (i.e., the inability of sysbox-mgr to deal properly with mounting kernel headers into sysbox containers in some scenarios).

I have a proper fix for the sysbox-mgr bug, for which I will open a PR this week. Therefore, I don't think the fix you propose in this PR is needed, and I prefer to not accept it as otherwise the test container (inside of which Sysbox is tested) will not look quite like a real host, but rather have unique mounts for each kernel header.