RFR: 1012: Lots of "unhealthy" jdk repos found in scratch dirs

[Erik Joelsson]

Add --dissociate when cloning a repo using a seed. It's simply not safe to share objects between repos when we remove objects in the seed repo (which happens automatically behind the scenes when git GCs). This is documented in the git-clone man page. Changing this will increase disk usage some, but that's something we just have to live with.

-------------

Commit messages:
 - SKARA-1012

Changes: https://git.openjdk.java.net/skara/pull/1146/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1146&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1012
  Stats: 4 lines in 2 files changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1146.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1146/head:pull/1146

PR: https://git.openjdk.java.net/skara/pull/1146