Fix non-portable code in hotspot shell tests in 8u

Some hotspot shell tests use "==" for comparison inside of "[ ]". However this is bash extension and it is not portable (posix test command only knows single "=", see: [1]).

This results in errors on systems where default shell is not bash, such as Ubuntu used in GHA (which defaults to "Dash" shell). Expressions are then treated as always false.

Problem is only present on 8u as newer jdks use different approach for shell/jni tests and no longer have these shell tests.

[1] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html