test, migrate tests to loading the fix50sp2 engine beforehand

Signed-off-by: Sebastian Freundt <freundt@fresse.org>
test, adapt fixc_from_fixml_01 test to engine loading, ...

This shouldn't be necessary as we're linking to the fix50sp2 engine
but malloc_perturb seems to bugger it up so we explicitly open it
again.

Signed-off-by: Sebastian Freundt <freundt@fresse.org>
Merge branch 'test/engdso' into next

* test/engdso:
  test, adapt fixc_from_fixml_01 test to engine loading, ...
  test, migrate tests to loading the fix50sp2 engine beforehand