fix(make.conf.user): Fix references to old make.conf.user path.

We've moved all of the chroot configs from /etc to /etc/portage but
setup_board was still symlinking to /etc. Fix the path so no one gets
mixed up by the two copies of the same file. Remove unused script that
also used to write to old location.
fix(setup_board): Install baselayout with USE=build

We need to install baselayout with the build use flag as the very first
package in the new board sysroot to ensure the system's directory
structure is created correctly. This should resolve surprise failures
with the bootengine ebuild.
fix(install_toolchain): Prevent tar from replacing lib symlinks

The cross toolchain doesn't have lib symlinks but this works because it
also doesn't install things to lib. However when this script manually
extracts the toolchain packages to BOARD_ROOT tar includes those empty
directories, replacing the symlinks that were previously there.

Longer term this really needs to go away, whatever build time is saved
by re-using the cross toolchain packages in BOARD_ROOT is not worth this
insane level of complexity it causes...
Merge pull request #50 from marineam/baselayout

Baselayout