use --select for our core packages

We are changing the default emerge options to use --oneshot, so make sure
our scripts select the packages we care about for @world.

BUG=None
TEST=setup_board+build_packages for tegra2 adds pkgs to world

Change-Id: I5fc68c538a1a1c846bd9724f27ef717029d11d42
Reviewed-on: https://gerrit.chromium.org/gerrit/16838
Reviewed-by: David James <davidjames@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/sdk_lib/make_chroot.sh b/sdk_lib/make_chroot.sh
index 10fe1f5..3491793 100755
--- a/sdk_lib/make_chroot.sh
+++ b/sdk_lib/make_chroot.sh
@@ -431,7 +431,7 @@
 early_enter_chroot $EMERGE_CMD --deselect dhcpcd
 
 info "Running emerge ccache curl sudo ..."
-early_enter_chroot $EMERGE_CMD -uNv $USEPKG $EMERGE_JOBS \
+early_enter_chroot $EMERGE_CMD -uNv $USEPKG --select $EMERGE_JOBS \
   ccache net-misc/curl sudo
 
 # Curl is now installed, so we can depend on it now.