Remove j2sdk and j2re nomenclature from build images

We should rename the build target directories as per discussion on build-dev mailing list ;
http://mail.openjdk.java.net/pipermail/build-dev/2013-November/011239.html

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Now that we've removed the old build system, can we please now
remove the last vestiges of Sun's pre-Java 5 naming scheme?

I refer in particular to these directories in a typical build:

  images/j2re-image
  images/j2sdk-image
  images/j2sdk-server-image

The "j2" nomenclature hasn't been used since 1.4.2. These should
be named "jre-image", "jdk-image", and "jdk-server-image".

Thanks,
- Mark
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