RFR: 7903097: jtreg could implement ToolProvider

[Christian Stein]

Implement `ToolProvider`, now that the main `jtreg` tool requires JDK >= 9.

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Commit messages:
 - Update more expected numbers
 - Expect another passing test
 - Re-use I18N messages by moving `JtregToolProvider` to `tool` package
 - Add rule to copy service-related resource files
 - 7903097: jtreg could implement ToolProvider

Changes: https://git.openjdk.java.net/jtreg/pull/54/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=54&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903097
  Stats: 111 lines in 7 files changed: 105 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/54.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/54/head:pull/54

PR: https://git.openjdk.java.net/jtreg/pull/54