Test fixtures changed to pointers.

Change the fixture types to pointers to structures that are heap allocated in the tests that use SETUP_TEST_FIXTURE.  This will permit error returns from the setup function and allow for future running tests in parallel.

Also removed a call of `exit(2)` which allows the remaining tests to run if one fails to initialise.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4071)