RFR: 7904021: Parsing group files(TEST.GROUPS) on non-UTF-8 encoding platforms fails with java.nio.charset.MalformedInputException

[Pasam Soujanya]

Parsing group files(TEST.GROUPS) on non-UTF-8 encoding platforms fails with java.nio.charset.MalformedInputException.

Error:
Error: Cannot read group files for /test/jdk: java.nio.charset.MalformedInputException: Input length = 1
---------
### Progress
- [ ] Change must be properly reviewed (1 review required, with at least 1 [Reviewer](https://openjdk.org/bylaws#reviewer))
- [x] Change must not contain extraneous whitespace
- [x] Commit message must refer to an issue

### Error
 ⚠️ The pull request body must not be empty.

### Integration blocker
 ⚠️ Title mismatch between PR and JBS for issue [CODETOOLS-7904021](https://bugs.openjdk.org/browse/CODETOOLS-7904021)



### Reviewing
<details><summary>Using <code>git</code></summary>

Checkout this PR locally: \
`$ git fetch https://git.openjdk.org/jtreg.git pull/267/head:pull/267` \
`$ git checkout pull/267`

Update a local copy of the PR: \
`$ git checkout pull/267` \
`$ git pull https://git.openjdk.org/jtreg.git pull/267/head`

</details>
<details><summary>Using Skara CLI tools</summary>

Checkout this PR locally: \
`$ git pr checkout 267`

View PR using the GUI difftool: \
`$ git pr show -t 267`

</details>
<details><summary>Using diff file</summary>

Download this PR as a diff file: \
<a href="https://git.openjdk.org/jtreg/pull/267.diff">https://git.openjdk.org/jtreg/pull/267.diff</a>

</details>

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

Commit messages:
 - Merge branch 'master' of github.com:psoujany/jtreg
 - Read InputStream in defaultCharset

Changes: https://git.openjdk.org/jtreg/pull/267/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=267&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904021
  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jtreg/pull/267.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/267/head:pull/267

PR: https://git.openjdk.org/jtreg/pull/267