RFR: 8285915: failure_handler: gather the contents of /etc/hosts file

[Jaikiran Pai]

Can I please get a review of this change which addresses https://bugs.openjdk.java.net/browse/JDK-8285915?

With this change, the environment details collected by the failure handler will now include the contents of the `/etc/hosts/` file, which can be useful in certain cases when debugging network tests that fail.

Testing done (on macOS):


cd test/failure_handler 
make test

Then verified that the generated environment.html had the `/etc/hosts` file content

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Commit messages:
 - 8285915: failure_handler: gather the contents of /etc/hosts file

Changes: https://git.openjdk.java.net/jdk/pull/8466/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8466&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285915
  Stats: 8 lines in 2 files changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8466.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8466/head:pull/8466

PR: https://git.openjdk.java.net/jdk/pull/8466