It turned out that the new make bootstrapping file Init.gmk needed some
redesign.
First of all, we should always respect the SPEC if possible, and not
chose a random configuration for extracting targets.
Secondly, tab completion did not work in a non-standard configuration
directory. (This is slightly related to the problem above.)
And third, there were still some code cleanup necessary.
Bug: https://bugs.openjdk.java.net/browse/JDK-8076465
WebRev:
http://cr.openjdk.java.net/~ihse/JDK-8076465-init-improvements/webrev.01
/Magnus
