RFR: JDK-8187544 Replace BUILD_OUTPUT and OUTPUT_ROOT with OUTPUTDIR.

Thu Sep 14 21:14:33 UTC 2017

Due to historical reasons, we have had two variables that points to the 
output directory (e.g. "$topdir/build/linux-x64"), one named 
BUILD_OUTPUT and one named OUTPUT_ROOT.

First of all, these two should be unified into one.

Second, it should be renamed OUTPUTDIR to better align with other 
variables such as TOPDIR, and the various *_OUTPUTDIR variables we 
already have.

The only non-trivial part of this patch was the handling in 
bootcycle-spec.gmk.in. I've verified that I can still build 
bootcycle-images.

Bug: https://bugs.openjdk.java.net/browse/JDK-8187544
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8187544-introduce-OUTPUTDIR/webrev.01

/Magnus