Uniform TEST_*() check usage in test/ectest.c

Uniform TEST_*() check usage in test/ectest.c

- Replace a `TEST_true()` with `!TEST_false()` to avoid reporting
  confusing errors
- We tend to use `if (!TEST_foo() || !TEST_bar())` and it's a bit
  confusing to switch to `if(!(TEST_foo() && TEST_bar()))`: replace it
  with the more common style

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/9813)