RFR: 7538: Check in launcher for JVMKeepAlive

[Marcus Hirt]

Helpful for new developers.

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Commit messages:
 - 7538: Check in launcher for JVMKeepAlive

Changes: https://git.openjdk.java.net/jmc/pull/368/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=368&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7538
  Stats: 19 lines in 1 file changed: 19 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc/pull/368.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/368/head:pull/368

PR: https://git.openjdk.java.net/jmc/pull/368