RFR: 7904084: Unset javaOpts and jtregOpts in jtreg.sh [v4]

[SendaoYan]

> Hi all,
> 
> In jtreg.sh it will combine all the java options and jtreg options in the `for i in "$@"` loop. SHELL use javaOpts and jtregOpts as global varable by default, this means jtreg.sh will receive the value of javaOpts and jtregOpts outside. I think this unexpected.
> To avoid this siutation, I think we should unset javaOpts and jtregOpts before use it.

SendaoYan has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'openjdk:master' into jbs7904084
 - Merge branch 'openjdk:master' into jbs7904084
 - Merge branch 'openjdk:master' into jbs7904084
 - 7904084: Unset javaOpts and jtregOpts in jtreg.sh

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

Changes:
  - all: https://git.openjdk.org/jtreg/pull/291/files
  - new: https://git.openjdk.org/jtreg/pull/291/files/fb3a5dd1..a3076f53

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=291&range=03
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=291&range=02-03

  Stats: 196 lines in 18 files changed: 162 ins; 5 del; 29 mod
  Patch: https://git.openjdk.org/jtreg/pull/291.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/291/head:pull/291

PR: https://git.openjdk.org/jtreg/pull/291