linux-build: move the build to fix install problems on the builder

When the directory the kernel was build with exists on install,
a symlink is used to it, and is used instead of the headers.
This is problematic because if the source is cleaned or reused,
any module build will fail.

To work around this we move the folder for the build and move it
back, and on install the pacakge manager removes the dodgy symlink
and uses the headers like it should.