scripts/oe-setup-builddir: make environment variable the highest priority source for TEMPLATECONF

This sets the following order:

1. TEMPLATECONF set in the unix environment (for example as a
prefix to '. oe-init-build-env').

2. If empty then $BUILDDIR/conf/templateconf.cfg

3. If absent then $OEROOT/.templateconf (oe-init-build-env sets OEROOT
to where it is, which is poky or oe-core).

I believe this is more logical and consistent with common practice;
it also avoids situations where the user is stuck with cryptic
errors because templateconf.cfg contains something invalid and
that something cannot be overridden from command line.

(From OE-Core rev: 7296c42b8c58e6e08f4210eb7b51d852b1ee950e)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-setup-builddir

@@ -38,7 +38,7 @@ chmod -st "$BUILDDIR/conf" 2>/dev/null || echo "WARNING: unable to chmod $BUILDD
 
 cd "$BUILDDIR"
 
-if [ -f "$BUILDDIR/conf/templateconf.cfg" ]; then
+if [ -f "$BUILDDIR/conf/templateconf.cfg" -a -z "$TEMPLATECONF" ]; then
     TEMPLATECONF=$(cat "$BUILDDIR/conf/templateconf.cfg")
     # The following two are no longer valid; unsetting them will automatically get them replaced
     # with correct ones.