RFR: JDK-8276202: LogFileOutput.invalid_file_vm asserts when being executed from a read only working directory

[Johan Sjölén]

This PR replaces some of the VM `assert` with gtest `ASSERT` where applicable and fixes a bug in a UL test.
The test used to create a temporary directory in cwd, failing if cwd is read-only. Now it creates the directory in /tmp/.

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Commit messages:
 - Generate temporary directory in tmp/
 - Replace VM assert with gtest ASSERT

Changes: https://git.openjdk.java.net/jdk/pull/8238/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8238&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276202
  Stats: 22 lines in 3 files changed: 14 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8238.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8238/head:pull/8238

PR: https://git.openjdk.java.net/jdk/pull/8238