[jdk11u-dev] RFR: 8314552: Fix javadoc tests to work with jtreg 7

[Aleksey Shipilev]

This is a variant of the fix for JDK 11u, required for jtreg upgrade.

Additional testing:
 - [x] `langtools:all` passes with jtreg-7.3.1+1 (some known failures fixed by other PRs)

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

Commit messages:
 - Backport e83046409d81d074cd68dc823e794a852ed93cee

Changes: https://git.openjdk.org/jdk11u-dev/pull/2557/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2557&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314552
  Stats: 14 lines in 5 files changed: 5 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2557.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2557/head:pull/2557

PR: https://git.openjdk.org/jdk11u-dev/pull/2557