Integrated: CODETOOLS-7902994: clean up `make sanity` target

[Jonathan Gibbons]

A change to cleanup the use of the `JDK`_N_`HOME` variables.

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Commit messages:
 - CODETOOLS-7902994: clean up `make sanity` target

Changes: https://git.openjdk.java.net/jtreg/pull/17/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=17&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-7902994
  Stats: 62 lines in 2 files changed: 53 ins; 3 del; 6 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/17/head:pull/17

PR: https://git.openjdk.java.net/jtreg/pull/17