Review Request: 8002028: build-infra: need no-hotspot partial build

[Erik Joelsson]

Adding support for importing the hotspot binaries from a prebuilt j2sdk 
image. Use configure option --with-import-hotspot=/path/to/j2sdkimage 
and the build will skip building hotspot.

http://cr.openjdk.java.net/~erikj/8002028/webrev.jdk.01/ 
<http://cr.openjdk.java.net/%7Eerikj/8002028/webrev.jdk.01/>
http://cr.openjdk.java.net/~erikj/8002028/webrev.root.01/ 
<http://cr.openjdk.java.net/%7Eerikj/8002028/webrev.root.01/>

Note that if trying this patch (or before committing it) make sure to 
regenerate configure first and if committing, commit in jdk/make/closed too.

/Erik