Jemmy tests are started in tools/make/build-template.xml @ 93:
    <exec executable="${env.SHELL}">
        <arg value="${jtreg.home}/bin/jtreg"/>
        ...

There is a similar spot in tools/Jemmy/JemmyFX/build.xml.

This runs jtreg through system's default shell. Because jtreg is an sh script, this means the test execution will not work on system which use a different default shell than sh or bash (ex. fish has different syntax).

SHELL is an env variable set by login processes, so we should avoid changing it. Because we cannot be sure that jtreg will be flagged as executable (might be manually built) we should instead use /bin/bash directly as the executable. README also recommends setting the SHELL env variable to /bin/bash, so this change should not present any problems.