layer.conf/bitbake.conf: Tweak PATH

layer.conf/bitbake.conf: Tweak PATH

We want the help2man script in scripts/ to be found in preference to any from
the host system and from the native sysroot. It turns out to be tricky to
get the order right from layer.conf so we move the addition of the scripts
directory to bitbake.conf.

Without this, "bitbake libtasn1 -c cleansstate; bitbake help2man-native; bitbake libtasn1"
will fail due to finding the host system help2man before ours.

(From OE-Core rev: 859255dd30958db018d40ede94a76db36a98da7f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>