[unittests] fix intermittent SupportTests failures

by invoking `SupportTests --gtest_shuffle=1`.

`HideUnrelatedOptions`/`HideUnrelatedOptionsMulti` failed due to other
tests calling `cl::ResetCommandLineParser()` which causes default
options to be removed.

`ExitOnError` would hang due to the threading environment. Renaming it
as `*Deathtest` is the recommended practice by GTest docs.