RFR: 7539: JDP Tests failing in VPN environments [v2]

[Johannes Bechberger]

> Only run broadcasting related tests when supported.
> Tested on Mac M1 with and without VPN.

Johannes Bechberger has updated the pull request incrementally with two additional commits since the last revision:

 - Add skip functionality to build.sh script
 - Introduce -DskipJDPMulticastTests

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/369/files
  - new: https://git.openjdk.java.net/jmc/pull/369/files/774c2093..a50e543f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=369&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=369&range=00-01

  Stats: 80 lines in 4 files changed: 41 ins; 16 del; 23 mod
  Patch: https://git.openjdk.java.net/jmc/pull/369.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/369/head:pull/369

PR: https://git.openjdk.java.net/jmc/pull/369